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Composite Structures
Journal Prestige (SJR): 1.905
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  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0263-8223
Published by Elsevier Homepage  [3159 journals]
  • Standard and boundary layer perturbation approaches to predict nonlinear
           axisymmetric behavior of cylindrical shells
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Famida Fallah, Ehsan Taati, Mohsen Asghari, J.N. Reddy The feasibility and performance of standard and boundary layer perturbation techniques in nonlinear analyses of cylindrical shells are investigated. To this end, the nonlinear axisymmetric behavior of short and long functionally graded (FG) cylindrical shells is considered. The nonlinear governing equations of shell theory with first-order approximation and the von Karman nonlinearity are decoupled. This uncoupling makes it possible to present an analytical solution. A new boundary layer perturbation solution is presented by reducing the governing equations to a normalized form of boundary-layer type. Also, the uncoupled governing equations are solved using standard one-, two-, and three-parameter expansions. Findings indicate that the boundary layer technique cannot predict the post-buckling behavior of cylindrical shells for any geometric ratios R/h andL/R, since after occurrence of instability, the behavior of shell is not boundary-layer type and it is impossible to satisfy the matching conditions. Hence, this technique is only valid for the analysis of long shells before buckling occurs. Furthermore, the standard perturbation series in terms of output parameters can predict the buckling load and the static equilibrium path with acceptable accuracy only under consideration of the deflection of points at an area near enough to the ends of the shell. On the other hand, the standard expansions in loading parameters are able to predict the snap-through post-buckling behavior accurately by considering higher-order terms (around 30th order) in expansion series.
  • Buckling analysis and control of layered electrode structure at finite
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Zuoquan Zhu, Hongjiu Hu, Yaolong He, Bo Tao This work has proposed a coupled mechanochemical model to investigate the buckling performance of electrode and thereby enhance the mechanical integrity of lithium-ion batteries. This method based upon finite deformation theory is capable to simulate the state of charge (SOC) and path dependent buckling phenomenon of the layered structure. It is revealed that the buckling behavior of an electrochemical loaded electrode depends not only on the material properties and the electrode geometry but also on the charging/discharging process, SOC as well as the operation current rate. Moreover, with regarding to the lithiation stiffening active material, the results show that increasing the current density in lithiation while decreasing it upon delithiation can increase the relatively critical buckling load, and contribute the electrode to withstand buckling failure. As for the lithiation softening one, it is disclosed that the bucking resistance would be impaired in lithiation and recovered upon full delithiation. In addition, to eliminate the adverse effect of lithiation soften on the electrode buckling resistance, design insights into the current collector have been provided.
  • Stress concentration in octagonal honeycombs due to defects
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Shengchao Ouyang, Zichen Deng, Xiuhui Hou Different kinds of defects will form in the Additive Manufacturing process for honeycomb structures, which will lead to reductions in the mechanical properties. Missing cell walls along one row for the octagonal honeycomb is one of the typical defect, resulting in great stress concentration. To solve this problem, the defect region is approximated by an elliptical hole, and analytic formula of tensile stress and empirical formula of bending stress for the cell wall closest to the defect region are proposed. Comparison with the FEM results, verifies the effectiveness of the proposed analytical method. Further, the numerical results reveal that the degree of the stress concentration is not only influenced by the number of missing cell walls but also related to the aspect ratio. In addition, the aspect ratio of cell wall has a negligible effect on the results of the tensile stress but can sensitively affect the bending stress.
  • Biomechanical design of a composite femoral prosthesis to investigate the
           effects of stiffness, coating length, and interference press fit
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Faris Tarlochan, Hassan Mehboob, Ali Mehboob, Seung-Hwan Chang Traditionally, high stiffness hip prostheses are associated with aseptic loosening. Hence, the effects of stiffness, coating length, and interference press fit on load sharing and micro-movements are investigated for a better understanding from a mechanical perspective. A simplified 3D model of the femur and prostheses composed of cobalt chrome (CoCr), titanium (Ti), and glass/polypropylene (Twintex [0]2nT) composite are constructed. Three interference fits corresponding to 5, 25, and 50 µm are used with half, three-quarter, and full lengths of coating that are used to assemble the prostheses with bones to investigate micro-movements at the bone-prosthesis interfaces, interfacial failure, and stress transfer to the bone. The reaction forces of body weight and muscular forces in the femur are used to simulate the FE model. The results indicate that the CoCr and Ti prostheses exhibit low micro-movements at the proximal end and high micro-movements at the distal end and vice versa for the Twintex [0]2nT composite prosthesis. Uniformity of stress transfer to the bone along the prosthesis efficiently increases with increases in the coating lengths and interference press fits for all the cases. A fully coated length of Twintex [0]2nT composite prosthesis with a 50-µm interference press fit provides the most efficient load sharing and stress transfer to the bone and micro-movements at the bone–prosthesis interface.Graphical abstractGraphical abstract for this article
  • On the analysis of non-homogeneous laminates using the refined zigzag
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Fernando G. Flores, Sergio Oller, Liz G. Nallim This work shows possibilities and limitations of the refined zigzag theory (RZT) that has been used in different structural (beam, plate and shell) finite elements. The refined zigzag theory can deal with composite laminates, adding only one nodal degree of freedom per spatial dimension of the laminate, obtaining very good accuracy. It assumes that the in-plane displacements have a piece-wise linear shape across the thickness depending on the shear stiffness of each composite layer. This paper presents the main aspects of a beam/shell of revolution element used for the numerical simulations. The details of the refined zigzag theory are given also in order to discuss some limitations that occur when dealing with the non-linear phenomenon of delamination. Two examples are presented and discussed, including different inhomogeneities that show the limitations of the RZT for the treatment of partially delaminated beams.
  • Nonlinear free vibration of functionally graded graphene platelets
           reinforced porous nanocomposite plates resting on elastic foundation
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Kang Gao, Wei Gao, Da Chen, Jie Yang This paper presents an investigation on free vibration of functionally graded (FG) porous nanocomposite plates reinforced with a small amount of graphene platelets (GPLs) and supported by the two-parameter elastic foundations with different boundary conditions. Four different porosity distributions of the parent metal were reinforced by four various GPLs dispersion patterns (evenly or unevenly) along the thickness direction. To obtain graded distribution in both porosity and GPLs, the Young’s modulus, shear modulus and density of nanocomposites are assumed to vary through the thickness direction due to variation of internal pores and the volume fraction of GPLs. By employing Halpin-Tsai micromechanics model, effective elastic modulus of the nanocomposites is obtained according to the assumption of closed-cell cellular solids under Gaussian Random Field scheme. The governing equations of FG GPLs-reinforced metal foams resting on elastic foundations are derived from Hamilton’s principle by the means of classic plate theory with the consideration of von Kármán strain-displacement relation. Applying the differential quadrature method, the dimensionless natural frequencies of porous nanocomposite plates with different boundary conditions are obtained and present method is thoroughly validated with the results in open literature. The comprehensive parametric studies on different porosity coefficients, GPL dispersion patterns, weight fraction of GPL, aspect ratios, thickness ratios and parameters of elastic foundation on free vibration of FG GPLs-reinforced porous plates with various boundary conditions. An interesting finding is that the increase of porosity coefficients would lead to the linearly decrease of both mass density and stiffness of the plates, but the increase of porosity coefficients does not always induce the decrease of natural frequencies. Moreover, both porosity distribution and GPL dispersion pattern have a distinct effect on dynamic characteristics, the former plays a more important role than the latter in analysing mechanical properties of FG GPLs-reinforced plates.
  • Interface finite elements for the modelling of constrained viscoelastic
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): L. Rouleau, A. Legay, J.-F. Deü Viscoelastic treatment has traditionally been used in industrial applications to reduce structural noise and vibration by dissipating part of the strain energy. Constrained-layer damping (CLD) treatments usually dissipate more energy than free-layer damping treatment (FLD), but its design must be integrated in the design process of the structure to be damped. Parametric studies are then necessary to determine the optimal viscoelastic material forming the CLD treatment, and the optimal placement and thickness of the layer. For structures with complex geometry, 3D finite elements are required and a change in the thickness or the placement of the viscoelastic layer implies a complete remeshing of the structure, which represents a significant additional computational cost in the parametric study. The goal of this work is to present a new strategy to model efficiently thin constrained viscoelastic layers. Two interface finite elements, based on a surface representation of the damping layer, are proposed. The first one is a joint element using relative displacements at the interface, and the second one is an original zero-thickness element which makes use of a volumetric integration. These elements are validated by comparison with 3D finite elements. Results show that the proposed interface elements allow a good representation of the damping layer’s behaviour, especially for thin layers. Moreover, this modelling approach can be efficiently used in the context of parametric optimisation.
  • Integration of material and process modelling in a business decision
           support system: Case of COMPOSELECTOR H2020 project
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Salim Belouettar, Carlos Kavka, Borek Patzak, Hein Koelman, Gast. Rauchs, Gaetano Giunta, Angela Madeo, Sabrina Pricl, Ali Daouadji This paper shares and contributes to a ground-breaking vision developed and being implemented which consists in the integration of materials modelling methodologies and knowledge-based systems with business process for decision making. The proposed concept moves towards a new paradigm of material and process selection and design by developing and implementing an integrated multi-disciplinary, multi-model and multi-field approach together with its software tool implementation for an accurate, reliable, efficient and cost effective prediction, design, fabrication, Life Cycle Engineering (LCE), cost analysis and decision making. This new paradigm of integrated material design is indeed endowed with a great potential by providing further insights that will promote further innovations on a broad scale.
  • A multi-scale stochastic fracture model for characterizing the tensile
           behavior of 2D woven composites
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): LiChuan Zhou, MingWei Chen, Chuang Liu, HengAn Wu In this paper, a multi-scale stochastic fracture model is presented to study the nonlinear mechanical behaviors of two-dimensional (2D) woven C/SiC composites under uniaxial tension. This model considers the randomly distributed intrinsic flaws and the complex braided structure of composites. In the model, the micro-scale representative volume element (RVE) is developed to compute the effective properties of yarns, which are then used in the meso-scale RVE to capture the macroscopic stress response of woven composites. Weibull distribution law is applied to the material elements to reflect the random flaws. The failure mechanism of composites is identified by analyzing the damage rates and the fracture morphologies of fiber, matrix, and interface. The effects of fiber volume fraction and temperature on fracture strength are predicted and the results demonstrate that the failure location varies as the temperature increase due to the relief of thermal residual stress. The presented model provides an efficient tool for evaluating the mechanical properties of textile composites.
  • Characterisation of composite elastic properties by means of a multi-scale
           two-level inverse approach
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Lorenzo Cappelli, Marco Montemurro, Frédéric Dau, Laurent Guillaumat This work deals with the problem of characterising the elastic properties of a composite material at both mesoscopic (ply-level) and microscopic (constitutive phases-level) scales. This goal is attained by means of an adequate multi-scale identification strategy (MSIS) which aims at identifying the constitutive properties, at each relevant scale, by exploiting the information restrained in the macroscopic dynamic response of the composite. In this background, the multi-scale identification problem is split into two interdependent sub-problems which are stated, at both levels, as constrained minimisation problems. At the first level the goal is the characterisation of the lamina properties by minimising the distance between the numerical and the reference harmonic responses of the composite. The second level problem aims at identifying the elastic properties of both fibre and matrix by minimising the distance between the effective elastic properties evaluated through a homogenisation process and those provided by the first-level inverse problem. The MSIS is based on a special global hybrid optimisation tool and on the strain energy homogenisation method of periodic media. Its effectiveness is proven through a meaningful benchmark.
  • Wind turbine blade trailing edge failure assessment with sub-component
           test on static and fatigue load conditions
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): F. Lahuerta, N. Koorn, D. Smissaert Wind turbine blades present different types of failure mechanisms and modes which are associated with specific loading conditions. Trailing edge failure mode has been documented in full-scale blade tests as one of the failure types observed in blades on service. Trailing edge failure is characterized by failure of the trailing edge adhesive joint and the buckling of the trailing edge sandwich panels. This failure is governed by the contribution of edgewise, flapwise and torsion moments, with edgewise moments being the main driver. This paper describes a blade sub-component test setup suitable for studying trailing edge failure on static and fatigue load conditions, which is an improvement in the experimental verification of a trailing edge blade design. The test setup and design drivers are described and studied via FE models. Static and fatigue test results are reported for a full-scale blade section sub-component obtained from a 34 [m] wind turbine blade. Moreover, experimental results are discussed and compared with FE models to describe and study the trailing edge failure mechanism.
  • Experimental and numerical investigation on assessing local bearing
           behavior of a pultruded GFRP bridge deck
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Haohui Xin, Ayman S. Mosallam, Yuqing Liu, Congzhe Wang, Jun He In this study, a methodology proposing size reduction of flat steel bearing plates that are commonly used in experimentally evaluating composite deck to transfer and distribute simulated vehicles loads to the top of bridge deck specimens is presented. The proposed methodology considers the tire-to-deck effects based on both a contact pressure distribution model and finite element (FE) simulation results. Ultimate capacity and associated failure modes for the following two loading cases: (i) moment-dominated, and (ii) moment-shear coupled loads were experimentally evaluated. Experimental results showed that the ultimate capacity for moment-dominated loading case is 35.60 kN, while capacity for the same composite deck when subjected to a moment-shear coupled load is 44.34 kN. Experimental results indicated that the initiation of failure for both loading cases was in the form of the development of longitudinal cracks at both top flanges and at outer web section near the loading side. Finite element models that consider lamina damage were developed and analyzed. A good agreement between numerical and experimental results is achieved.
  • Quantifying the orthotropic damage tensor for composites undergoing
           damage-induced anisotropy using ultrasonic investigations
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Louise Olsen-Kettle We quantify the evolution of the general fourth order damage tensor for initially orthotropic composites undergoing damage-induced anisotropy using ultrasonic investigations. Two of the most challenging problems which arise in continuum damage mechanics are firstly the selection of variables to describe the internal damage and secondly the difficulty in modelling materials with significant initial anisotropy such as composites. This research helps advance models of anisotropic damage to overcome both these challenges. We demonstrate how to identify the directionality and magnitude of the introduced damage using experimental ultrasonic measurements of damaged elastic moduli for initially anisotropic materials. This analysis provides a robust way to validate and advance models based on continuum damage mechanics and develop phenomenological models of anisotropic damage evolution for initially orthotropic materials.
  • Static and dynamic analysis of composite box beam based on geometrically
           exact nonlinear model considering non-classical effects
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Dan Luo, Yifeng Zhong, Boshu Li, Bin Deng In order to accurately predict the static and dynamic behavior of composite box beam, the Geometrically Exact Nonlinear Model (GENM) of composite box beams with arbitrary material distribution and large deflection was performed based on the Hodges’ neralized Timoshenko beam theory. The strain of any point in the deformed beam was calculated by the rotational tensor decomposition. Then, the asymptotic variational method was used to determine the arbitrary sectional warping. The generalized Timoshenko strain energy was derived from the second-order asymptotically exact strain energy using the equilibrium equation. The motion equations of GENM were established by using the Hamilton’s generalized principle. Finally, the proposed model was applied to the static and dynamic analysis of the composite box beam and verified by comparison with the experimental data. The influence of non-classical effects of sectional warping and transverse shear deformation on the composite box beam were further investigated. The results show that the sectional warping has significant effects on the static deformation and natural frequencies of composite box beams, and the influence of transverse shear deformation on the static deformation and the natural frequencies are related to the aspect ratio of beam length to section dimension.
  • A Timoshenko like model for piezoelectric energy harvester with shear mode
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Shreya Banerjee, Sitikantha Roy In the present study a fully coupled electromechanical Timoshenko beam theory is developed for modelling an energy harvester operating in d31 (flexural mode with correction due to shear deformation/rotary inertia) and relatively rare d15 (pure shear) mode. The model is developed based on Variational Asymptotic Method (VAM). VAM is a dimensional reduction methodology, which asymptotically approximates the original 3D electromechanical enthalpy into an equivalent 1D electromechanical enthalpy functional, using small parameters present in the system. Firstly, we develop a fully coupled Timoshenko cross sectional model, which provides us a single common platform to analyze both d15 and d31 mode energy harvester. The developed cross sectional model is represented by a 7 × 7 electromechanical stiffness matrix with an additional 1D electrical variable along with 6 1D mechanical degrees of freedom commonly present in Timoshenko type analysis. The cross-sectional model is general enough to accommodate harvesters made of multilayer, arbitrary shaped cross-section, anisotropic material operating in both pure shear as well as in flexure mode. The coupled cross sectional output is fed subsequently into a 1D beam problem for a complete solution.
  • Emergence of pseudo-ductility in laminated ceramic composites
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Sanjeev Kumar, Bensingh Dhas, Debasish Roy In this article, we explore the origins of pseudo-ductility in the inelastic response of laminated ceramic composites. By pseudo-ductility, we mean the engineered ductility of ceramic laminated composites by a strategic placement of the weak interfaces. For purposes of modeling, a phase field based brittle fracture approach is adopted and we use it to numerically study the response of such composites. This approach has the advantage of seamlessly modeling the growth of cracks through the interface as well as into the lamina. A finite element implementation of this brittle fracture model is carried out, using which the response of laminated ceramics is computed and compared with available experimental evidence in the literature. This implementation is also used to study the influence of geometric and material properties on the response, especially the damage propagation through ceramic laminates. Along with important geometric aspects such as the lamina thickness distribution and interface geometry, we also study how material properties like Young’s modulus and critical energy release rate of the interface may play a role in the engineered pseudo-ductility.
  • Effect of steel fibres on fracture parameters of cementitious composites
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Su-Jin Lee, Yerin Hong, Ah-Hyeon Eom, Jong-Pil Won This study was aim to determine the influence of the type of steel fibres on fracture parameters of cementitious composites. Flexural strength test was performed on notched beams according to EN 14651. Both type of steel fibre; arched- and hooked-end-type were added 10, 30, 40, and 50 kg/m3 as volume fractions. Steel fibres bridged the cracks during loading to fibre-reinforced cementitious composites, and prevented fracture rapidly. The load-deflection curve was depended on the shape and the quantity of the used fibres. The fracture energy absorption behaviour of arched-type steel fibre cementitious composites (ASFRC) was evaluated by applying different approach with a variety of fracture parameters such as stress intensity factor (KIC), energy release rate (GIC), the unit work in destruction (JIC), residual flexural tensile strength (fR,j), equivalent flexural strength (feq,j), and fracture energy (GF). As results, all fracture parameter was increased with fibre volume fraction up to 40 kg/m3. And ASFRC had higher value for these values than reinforced with hooked-end-type steel fibre (HSFRC); i.e. GF of ASFRC was 1.34–2.98 times higher compared to HSFRC.
  • An experimental investigation on high velocity impact behavior of
           hygrothermal aged CFRP composites
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Lulu Liu, Zhenhua Zhao, Wei Chen, Chao Shuang, Gang Luo In order to obtain the effect of hygrothermal aging on the high speed impact resistance of carbon fiber reinforced composites (CFRP), ballistic impact tests using flat blades projectile were conducted on the T700/TDE-85 laminates subjected to artificial accelerated hygrothermal aging (70 °C, RH95%) for different durations. Short beam shear tests were conducted on the aged specimens to evaluate the interfacial properties degradation. The effect of hygrothermal aging on the energy absorption and ballistic limit of composites were discussed. It is shown that the moisture absorption rate of the composites is in agreement with Fick law, with an equilibrium moisture absorption rate of 0.74% at 1369 h. The interlaminar shear strength (ILSS) descends rapidly with aging time and the retention rate of interlaminar shear strength was 50.6% after 2000 h. The ballistic limit and the critical energy absorption of the composites declined notably with the increase of aging time. Due to the weakened fiber/matrix interface, the delamination failure area in rhombic shape is of increasing severity with aging time. The matrix cracking and fiber/matrix interface debond due to long-term exposure to hygrothermal environment reduce the high velocity impact resistance of the composites.
  • Compressive behavior of hybrid double-skin tubular columns with a
           rib-stiffened steel inner tube
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Kaidi Peng, Tao Yu, Muhammad N.S. Hadi, Le Huang Hybrid fibre-reinforced polymer (FRP)-concrete-steel double-skin tubular columns (DSTCs) consist of an outer FRP tube and an inner steel tube, with the space inbetween filled with concrete. In hybrid DSTCs, the outward buckling of the steel inner tube is constrained by the surrounding concrete and the outer FRP tube, but its inward buckling is still possible. Existing research has shown that such inward buckling can become significant in non-circular hybrid DSTCs due to the non-uniform confinement, in hybrid DSTCs with a strong FRP tube due to the large axial deformation of the columns, and/or in hybrid DSTCs with a thin steel tube. In these cases, the stiffening of the inner steel tube is necessary to prevent or delay its inward buckling and to minimize its negative consequences to the column behavior. Against this background, a variation of hybrid DSTCs (hybrid R-DSTCs), in which the inner steel tube is stiffened by a number of vertical rib stiffeners, was recently developed at the University of Wollongong, Australia. This paper presents an experimental study on the axial compressive behavior of the new form of columns. The experimental program included a total of 12 R-DSTC specimens and two DSTC specimens for comparison, with the test variables being the number, thickness and width of rib stiffeners as well as the number of plies of fibres in the FRP tube. The test results confirmed that the additional rib stiffeners on the steel tube are effective in delaying the local buckling of the steel tube and in improving the performance of the columns. The test results also clarified the effects of the tested parameters of the rib stiffeners.
  • Effect of mechanical fastening pressure on the bond behaviors of
           hybrid-bonded FRP to concrete interface
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Yingwu Zhou, Xiaowei Wang, Lili Sui, Feng Xing, Zhenyu Huang, Cheng Chen, Pengda Li, Liu Mei Premature debonding failure of fiber-reinforced polymer (FRP) laminate is a primary reason for an accelerated onset of low working stress in the FRP of reinforced concrete (RC) structures strengthened with externally bonded (EB) FRP. Hybrid-bonded (HB) FRP can effectively prevent the debonding failure of FRP, leading to a significant enhancement in the ultimate strength of the HB-FRP system. The HB-FRP method mainly relies on external positive pressure provided by the anchoring device to improve the interfacial bond strength. Therefore, the magnitude of the positive pressure determines the strengthening effect of the anchoring system. This paper first optimizes the existing HB mechanical anchoring device. The positive pressure exerted on the FRP was adjusted by varying the torque to the anchoring device. The optimized anchoring device was used to study the bond behavior of the FRP-to-concrete interface under different torques. The test results showed that the debonding stress could be regulated by adjusting the torque, leading to a change in failure mode of the FRP-concrete interface. With the increase of torque, the utilization rate of FRP and ductility increased. When the torque was higher than a certain threshold, the FRP ruptured, after which, the continuously applied torque had no significant effect on the FRP-concrete interfacial bond behavior. Based on the experimental results, an ultimate bond strength model of the FRP-to-concrete interface under different torques was developed. Compared to the experimental results, the model showed satisfactory accuracy.
  • On fabric materials response subjected to ballistic impact using
           meso-scale modeling. Numerical simulation and experimental validation
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): E. Giannaros, A. Kotzakolios, G. Sotiriadis, S. Tsantzalis, V. Kostopoulos Present work investigates the dynamic response of dry fabric materials subjected to ballistic impact loading. The purpose of this research is to simulate the dynamic fabrics behavior accurately in order to capture the maximum fabric deformation, the ballistic limit and the absorbed energy in case of fabric perforation. In particular, a meso-scale modeling approach was employed to capture the behavior of para-aramid fabrics using LS-DYNA software. The quasi-static mechanical properties of fabric yarns were defined by standard tensile tests, whereas the Johnson-Cook strain rate rule was applied to approximate the strain rate dependence of yarn tensile strength. The numerical results were validated against impact experiments using air-gun apparatus.
  • A refined quasi-3D zigzag beam theory for free vibration and stability
           analysis of multilayered composite beams subjected to thermomechanical
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Bin Han, Wei-Wei Hui, Qian-Cheng Zhang, Zhen-Yu Zhao, Feng Jin, Qi Zhang, Tian Jian Lu, Bing-Heng Lu A refined four-unknown quasi-3D zigzag beam theory is developed to model the free vibration and buckling behaviors of multilayered composite beams subjected to axial mechanical loading (e.g., distributed load and terminal force) and uniform temperature variation. Types of the composite beams considered include laminated composite beams, sandwich beams with composite face sheets, and fiber metal laminates. The proposed theory accounts for not only thickness stretching but also interlaminar continuity of transverse shear stresses and displacements. Associated eigenvalue problems for various boundary conditions are derived using the Ritz method. Accuracy and effectiveness of the theoretical predictions are verified by comparison with existing results and present finite element simulations. The theory is employed to quantify the effects of axial distributed load/terminal force and temperature variation on free vibration and buckling for different boundary conditions, geometric parameters and material properties. The present theory could produce sufficiently accurate predictions of natural frequencies and buckling capacities of multilayered beams at a very low computational cost.
  • Analysis of the micro-cracking behaviour of carbon fibre reinforced
           flywheel rotors considering residual stresses
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): I. Koch, G. Just, F. Otremba, M. Berner, M. Gude The main challenge in today’s power grid management is the inclusion of renewable energy sources with inconstant energy production such as wind and solar plants and modern high technology fabrication or electric transportation with their uneven power consumption. For that purpose energy storage systems, such as high efficiency flywheels, with extraordinary cycle stability and charging-discharging rates are needed. Here carbon fibre reinforced composites play an important role as rotor material. In this study the cracking behaviour of helical layers of a cylindrical flywheel rotor is analysed under consideration of fabrication induced residual stresses and their viscoelastic reduction over long term storage. Based on static and fatigue experiments with crack counting inspections a finite fracture model is identified and calibrated for modelling the damage behaviour of flywheel rotors under cyclic loading.
  • Multiscale modeling of the mechanical properties of Nextel 720 composite
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Seyed Mohammad Mahdi Zamani, Kamran Behdinan The mechanical behavior of Nextel 720 ceramic matrix composite fibers was modeled using a novel multiscale modeling technique called the Bridging Cell Method (BCM). The BCM divides the system into three domains: atomistic, bridging, and continuum; with seamless coupling between the atomistic and continuum domains. The BCM allows considering the effects of the nano- and micro-structural characteristics of the material when modeling a macro-scale bulk. It incorporates interatomic potentials and quasi-harmonic calculations to find the final state of the system. The mechanical properties of the as-received fibers were investigated in tension via microtesile testing. The experimental results – evaluated in terms of the ultimate tensile strength, failure strain, and elasticity of the fibers under uniaxial loads – stood within the range reported in the literature; these results were then used to validate the Nextel BCM model. The Nextel BCM was conducted in two steps. First, the atomistic structure was relaxed. Then, a nano-crack was introduced in the mullite/alumina interface and the structure was pulled under a uniaxial tensile load until failure occurred. The BCM results indicated a good match between the Nextel BCM model and the experimental results. The validated Nextel BCM model can be used for the structural analysis of fibers.
  • Validation of the multi-objective structural optimisation of a composite
           wind turbine blade
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): E.M. Fagan, O. De La Torre, S.B. Leen, J. Goggins Structural optimisation of a wind turbine blade is presented in this work. The optimisation was performed using a multi-objective genetic algorithm and finite element modelling to determine the optimal structural design for a glass fibre-reinforced polypropylene composite blade. A candidate blade design from the Pareto efficient set was manufactured and tested for a range of structural characteristics, including: mass, centre of gravity, deflections, strains and natural frequencies. Static testing was carried out using a Whiffle tree test rig and a laser scanner was used to determine the deflection of the blade to a high degree of accuracy. The finite element model results for the custom-made design are compared to the measured blade response. The FE model predictions for strains, mass and natural frequencies are in relatively good agreement with the test results; however, notable deviations in the deflections predictions are attributed to modifications to the blade for manufacture and the shell-based modelling approach. The differences are discussed in detail and recommendations for future design work are outlined. The test results of the bespoke blade are also compared to two additional designs to determine the level of improvement afforded by the genetic algorithm approach. The bespoke glass fibre blade demonstrated an improvement in tip deflection of 16% relative to the original blade design, with a slight decrease in mass.
  • An improved Wittrick-Williams algorithm for beam-type structures
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Fei Han, Danhui Dan, Wei Cheng, Zang Jubao With the help of the dynamic stiffness method, the problem of dynamic characteristics analysis of an engineering structure can be transformed into the problem of solving the transcendental frequency equation. The Wittrick-Williams algorithm can provide the upper and lower bounds of any given modal frequency, so that the numerical solution of the equation can be obtained. However, for a complex beam-like structure, the method is no longer suitable because it is difficult to determine the corresponding the clamped-clamped frequency. For this reason, this paper proposes an improved Wittrick-Williams algorithm—hypothetical structure method, which calculates the clamped-clamped frequency count of the original structure indirectly through the “hypothetical structure” so that the dynamic characteristics analysis problem of the complex beam-like structure can be solved. Two typical beam structure examples and a complex double beam-like structure example are used to verify the accuracy and effectiveness of the proposed method.
  • On manufacturing constraints for tow-steered composite design optimization
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Timothy R. Brooks, Joaquim R.R.A. Martins Automatic fiber placement machines have made it viable to manufacture composites where fiber angles vary continuously—tow-steered composites. The additional freedom provided by tow-steered composites has the potential to increase structural performance; however, this approach comes with added design complexity. Numerical optimization can address this complexity, though it is critical that constraints are enforced to ensure that the resulting optimal tow-steered designs are manufacturable using current automatic fiber placement machines. In this work, we consider two manufacturing constraints: tow path curvature and gaps/overlaps. To develop these constraints, we consider a general tow-steered layer pattern as a 2D unit vector field, where the field streamlines represent the tow paths laid down by the automated fiber placing machine. This mathematical formulation provides a relationship between tow path curvature, gap/overlap propagation rate, vector curl, and divergence. These relationships also lead to a constraint on the minimum cut/add length of a tow for a given tow-steered pattern. We demonstrate the developed constraint formulations on two analytical examples, as well as on a structural optimization. We also explore the relationship between curl and divergence of rotated tow patterns. This analysis leads to the conclusion that layups featuring such patterns require strict constraints on bounds to ensure satisfaction of manufacturability requirements. Finally, we use these relationships to motivate a family of gap/overlap-free and curvature-free tow-steered patterns.
  • Filament-wound composite sleeves of permanent magnet motor rotors with
           ultra-high fiber tension
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Lei Zu, Hui Xu, Bing Zhang, Debao Li, Huabi Wang, Bin Zi Ultra-high fiber tension can provide sufficient compressive stresses to retain the permanet magnets mounted on the surface of the spindle. Therefore, a filament-wound sleeve with ultra-high fiber tension is designed to provide the radial compressive stress on the permanent magnet. Based on the elasticity theory, an approach for calculating the fiber stress distributions of composite layers and the radial compressive stresses on permanent magnets under different winding tensions are presented. The maximum winding tension of carbon fibers and the radial compressive stresses of composite layers are obtained by experiments. The fiber stresses of winding layers at the end of winding process under various winding tensions are calculated using the analytical method and finite element method, respectively. The results indicate that the analytical method can accurately predict the fiber stress distribution of the sleeve at the end of winding process and the radial compressive stresses on permanent magnets. The results obtained using the analytical method and the ones using the finite element method have a good agreement. The comparison between the analytical and experimental results is within the acceptable error. Therefore, filament-wound sleeves with ultra-high fiber tensions can satisfy the design requirements of high-speed permanent magnet rotors.
  • Structural applications of fibre reinforced polymer (FRP) composite tubes:
           A review of columns members
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Ali Umran Al-saadi, Thiru Aravinthan, Weena Lokuge Use of fibre reinforced polymer (FRP) in column applications is increased because it can act as a confining material, a reinforcement and a structural column. The application of FRP tubes is correlated with the fibre orientation since tube stiffness is mainly attributed to the stiffness of fibres. Thus, for confinement, the fibres should align in the transverse direction of the tube while they should align in the axial direction when tubes are used as compression members. FRP tubes with fibres mainly in axial direction may reach failure because the stiffness in the perpendicular direction to fibres depends only on the stiffness of the matrix. In order to boost the stiffness in the secondary direction while supporting fibres in the main direction, fibres should be in multi-directions.This paper reviews and identifies gaps in knowledge on the use of FRP materials in column applications in new or existing construction regimes.
  • Modelling delamination migration using virtual embedded cohesive elements
           formed through floating nodes
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): X.F. Hu, X. Lu, T.E. Tay Delamination migration is a common failure mode for composite laminates and the modelling technique remains challenging. For a complete progressive failure modelling, failure modes including delamination, matrix cracking, and the interaction between them should necessarily be considered. Existing methods may be effective for delamination or matrix cracking, but the situation becomes difficult when all of these failure modes are considered together in a unified framework. In this study, a new numerical framework based on floating node method is proposed to study delamination migration problem. A few discrete cohesive cracks are inserted into one element to offer multiple optional crack paths. Crack propagation due to delamination and matrix cracking can be modelled without remeshing. Element partition is treated in a convenient way which has simplified the implementation. And severe distortion of sub-element which may arise in a traditional element partition algorithm can be avoided. The proposed method is implemented through the ABAQUS user subroutine UEL and validated by comparing with experiments. The proposed numerical method has provided a framework for the modelling of delamination migration and also explored a method to model multiple discrete cracks within one element.
  • Mode-II interlaminar fracture and crack-jump phenomenon in CFRP composite
           laminate materials
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): S.S. R. Koloor, M.N. Tamin An interlaminar crack-jump event is one of the complex failure phenomena in laminated composite structures. This paper examines the mechanics of the interlaminar damage process leading to crack-jump event in CFRP composites under mode-II loading condition. A series of end-notched flexure tests of CFRP composite were conducted to create a standard interface failure, and an unstable interface fracture that led to crack-jump event. FE simulation of the composite tests was created using a new FE model-based construction and CZM theory in combination with a hybrid experimental-computational approach to assess the interface damage and crack-jump events. The FE model of the standard test predicted a short range crack-jump event instead of a gradual interface crack growth, coincided with the load drop in the structural response. A constant value of interface damage dissipation was predicted at the time of fracture for all composite cases. The unstable crack-jump event occurred due to the release of high strain energy in the composite structure while the interface underwent cracking process.
  • A review of micromechanics based models for effective elastic properties
           of reinforced polymer matrix composites
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Benjamin Raju, S.R. Hiremath, D. Roy Mahapatra Micromechanics based models are used for predicting the effective mechanical properties of reinforced polymer matrix composites. This paper reviews micromechanics based models for fiber reinforced polymer composites starting with the bounds established by Voigt and Reuss models, Hashin-Shtrikman model and then on to well-known micromechanics based models like Mori-Tanaka model, Self-consistent model and Differential scheme based models. The main objective is to critically review the areas in which these micromechanics based models hold good and analyse the limitations of these models. One of the limitations of the above mentioned models is the assumption of dilute dispersion and this is overcome in this paper by revising the Mori-Tanaka model by combining the differential scheme with Eshelby’s model to take into account the non-dilute dispersion effect. Numerical results are verified by finite element based simulation of the representative volume element (RVE). Experiments were carried out to estimate the effective elastic constants for different fiber volume fractions. Theoretical results are reviewed with reference to experimental measurements.
  • Innovative evolution of buckling structures for flexible electronics
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Duck Weon Lee, Jung Han Lee, Joon-Hyung Jin A buckling structure is a crucial element for materials used in wearable electronics by taking a topographical approach to solve a spatial constraint. This review introduces various buckling structures, with the corresponding theory and fabrication, for the latest materials or devices, including secondary batteries, supercapacitors, sensors, organic thin film transistors, polymer light-emitting diodes, and organic light emitting diodes, all of which have attracted much attention recently in journals. This review demonstrates how various buckling structures can be practically integrated into functional materials to enlarge the active area, to enhance flexibility or stretchability, and to improve unique functionality itself without loss.
  • Complex vibration modes in magnetorheological fluid-based sandwich beams
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Mateusz Romaszko, Bogdan Sapiński, Jacek Snamina The study investigates the complex vibration modes of sandwich beams filled with magnetorheological fluids (MRFs). An approach is suggested involving both experiments and calculation procedures to determine the complex modes of the beams’ free vibrations. Testing was done on three-layered cantilever beam filled with MRF and exposed to the magnetic field generated by an electromagnet. The purpose of the work is to analyse the influence of MRF on the beam motion and to determine the complex modes. Measurements of free vibrations of two beams filled with MRFs differing in the iron particle content by volume were taken in a purpose-built experimental set-up. Vibrations of the beam were registered under magnetic field varying in strength and for varied electromagnet’s positions with respect to the beam fixed end. Thus obtained measurement data were utilised to derive the dependence of magnetic field strength and electromagnet position on beam stiffness and damping. Complex modes were obtained with the use of finite element (FE) proposed by the authors for the investigated beams. Results are given as plots of modulus and argument of the complex vibration mode against the co-ordinate defining the position along the beam axis. Results revealed major discrepancies between the values of real and imaginary parts of the beams’ vibrations modes.
  • Modulus of elasticity in three- and four-point bending of wood
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Marián Babiak, Milan Gaff, Adam Sikora, Štepán Hysek This article deals with the difference in elasticity moduli of the three- and four-point bending of spruce and oak wood. Theoretical analyses of both loading methods are given. The measured characteristics were the MOR and MOE. The samples moisture content (MC) was 0, 8, 16, fibre saturation point (FSP),>FSP (after being soaked in water). We performed the measurements according to standard [1]. The results were evaluated using standard statistical methods. The outputs of this article broadens the knowledge of the properties of wood and can help in the creation of our theoretical models of these properties.
  • A new approach for forming polymeric composite structures
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): G. Ambrogio, R. Conte, F. Gagliardi, L. De Napoli, L. Filice, P. Russo The use of composite structures is increasing constantly in the last years, pushed by advantages of reduced weight and high strength. Moreover, the recent scenario points out a great attention on thermoplastic matrix composites due to their intrinsic recyclability as well for their possibility to re-use and re-manufacturing. However, the adoption of these materials can be further appreciated considering the secondary material workability as far as by demonstrating the possibility to re-manufacture the thermoplastic composite.The proposed work presents an experimental analysis carried out to investigate the downstream workability of a thermoplastic composite by one of the most versatile and flexible process. Glass fiber reinforced Polyamide 6 is the investigated material and the Single Point Incremental Forming is the implemented manufacturing approach. Since the composite matrix is characterized by a glass transition temperature higher than 50 °C, an external heating source has been necessary to perform the process in “hot” conditions. The process feasibility was fully demonstrated as well as the same was optimized in order to derive proper guidelines that can drive the process designer in the method star-up.
  • Axisymmetric auxetics
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): V.H. Carneiro, H. Puga Auxetic materials expand/contract transversely while tensioned/compressed in the longitudinal direction, thus they possess a negative Poisson’s ratio. According to the theory of elasticity, their existence in isotropic forms is theoretically possible, however, they are found in nature only in anisotropic forms. Auxetics are expected to possess enhanced relative static and dynamic properties, thus, several auxetic composites have been proposed and manufactured to mimic such behavior. This study shows the development of axisymmetric auxetics, a novel class of negative Poisson’s ratio composites obtained by the revolution of reentrant lattices in turn of an axis. It is shown by experimental testing and FEA that an auxetic circumferential deformation mechanism increases the overall Poisson’s ratio and promotes an elevation of the Specific Young’s modulus relative to regular honeycombs. Furthermore, the developed composites are compared in terms of Specific Young’s modulus and densities to commercial foams and other non-stochastic auxetics. It is concluded that they present enhanced specific properties for relative densities in the range of 0.28–0.35 and may be a promising route for future applications.
  • Compressive behavior of ultra-high performance fiber-reinforced concrete
           (UHPFRC) confined with FRP
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Weiqiang Wang, Chengqing Wu, Zhongxian Liu, Honglan Si This study presents the results of an experimental program on the compressive behavior of fiber reinforced polymer (FRP) confined ultra-high performance fiber-reinforced concrete (UHPFRC). A total of 38 specimens were prepared and tested under axial compression. In addition to FRP confined UHPFRC, FRP confined ultra-high performance concrete without fiber addition (UHPC), high strength concrete (HSC), and normal strength concrete (NSC) were also tested to investigate their comparative performances. The test results indicate that the FRP confined UHPFRC can exhibit ductile behavior if sufficient FRP confinement is provided. However, due to their ultra-high strength as well as the unique microstructure, FRP confined UHPFRC is likely to exhibit more brittle behavior than FRP confined NSC and HSC. Compared to FRP confined NSC and HSC, the confinement efficiency is less for FRP confined UHPFRC. Sudden stress reduction or stress fluctuations are observed shortly after the initial peak stress (axial stress at the first peak point) for FRP confined UHPFRC. Based on the confinement level, the stress-strain behavior of FRP confined UHPFRC may experience a second ascending branch or a continuous descending branch after the sudden stress reduction or stress fluctuations. The influences of FRP layers, FRP types, and fiber addition on the compressive behavior of FRP confined UHPFRC are observed to be significant. Moreover, existing stress-strain models available for FRP confined UHPFRC are evaluated by using a database collected in this study.
  • Influences of fabric density on mechanical and moulding behaviours of 3D
           warp interlock para-aramid fabrics for soft body armour application
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Mulat Alubel Abtew, François Boussu, Pascal Bruniaux, Carmen Loghin, Irina Cristian, Yan Chen, Lichuan Wang For the past many decades’ enormous research has been done on mechanical and moulding properties of 2D woven and non-woven fabrics. The current paper presents a comprehensive investigation of the tensile, bending and moulding behaviours of 3D orthogonal warp interlock fabrics with different fabric densities. Four 3D warp interlock fabrics with different areal density made from 168Tex linear density p-aramid Kevlar yarn were manufactured on dobby loom in GEMTEX laboratory. Based on the investigation both fabric density and yarn density shows a significant effect on bending and tensile properties of the fabrics. The bending rigidity in the warp and weft directions become higher in preforms with denser weft and warp yarn densities respectively. In general, as the yarn density in the respective warp or/and weft direction increases, the maximum tensile load with maximum strain increases. Moreover, the fabric and yarn density has also shown a great impact on various mouldability characteristics of 3D warp interlock preforms while deformation. The study finally elucidated that, like other parameters, fabric and the yarn density of 3D warp interlock influenced greatly the tensile, bending and moulding properties where those parameters should be considered carefully while applying in various technical textile applications i.e., soft body armour.
  • Composite repair patch evaluation using pulse-echo laser ultrasonic
           correlation mapping method
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Young-Jun Lee, Jung-Ryul Lee, Jeong-Beom Ihn Composite patch bonding repair is widely applied to metal and composite aircraft repair owing to its light weight and high resistance to fatigue and corrosion. However, composite patch repairing is done by vacuum bag processing in general, and the process itself is susceptible to manufacturing defects. In addition, the composite repair patches require more frequent inspections owing to the difficulty of the damage prediction. In this paper, we propose pulse-echo laser ultrasonic correlation mapping for a rapid quality evaluation method of composite repair patching. This method uses a pulse-echo ultrasonic propagation imaging system as a tool for in-situ and full-field inspection, and an ultrasonic correlation mapping (UCM) method was developed for fast and straightforward defect visualization. Two composite patch repair specimens were tested, and then UCM results were compared with other results using existing visualization methods. We also tested a composite laminate plate to verify the applicability of UCM to general composite parts. The UCM results showed similar or better performance than current visualization methods in all cases. Test results showed that the proposed system is suitable for both in-process quality evaluation and in-service field inspection.
  • Full field computing for elastic pulse dispersion in inhomogeneous bars
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): A. Berezovski, R. Kolman, M. Berezovski, D. Gabriel, V. Adámek In the paper, the finite element method and the finite volume method are used in parallel for the simulation of a pulse propagation in periodically layered composites beyond the validity of homogenization methods. The direct numerical integration of a pulse propagation demonstrates dispersion effects and dynamic stress redistribution in physical space on the example of a one-dimensional layered bar. Results of numerical simulations are compared with the analytical solution constructed specifically for the considered problem. The analytical solution as well as numerical computations show the strong influence of the composition of constituents on the dispersion of a pulse in a heterogeneous bar and the equivalence of results obtained by two numerical methods.
  • Hole-quality evaluation in drilling fiber-reinforced composites
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Andrew Hrechuk, Volodymyr Bushlya, Jan-Eric Ståhl This paper presents a novel approach for a complex evaluation of the quality of drilled holes in fiber-reinforced composite materials. The proposed methodology is based on non-destructive quantification of visible defects based on the numerical analysis of drilled hole images. Automatic contour definition and profile formation for the uncut fibers and delamination were implemented via modularized algorithms. Four criteria for the evaluation of the defect height and width distribution were developed and combined into an overall quality parameter, Q. The methodology was validated experimentally by drilling carbon-fiber-reinforced polymer (CFRP) samples with a cemented carbide drill bit. The results showed a linear relation between the hole quality Q, the drilled hole number, and tool wear.
  • Fracture plane based failure criteria for fibre-reinforced composites
           under three-dimensional stress state
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): N. Li, J.F. Gu, P.H. Chen Fracture plane based failure criteria for fibre-reinforced composite materials under three-dimensional stress state are presented. The failure function is taken as a polynomial expansion in terms of the stress components on fracture plane, which provides a general mathematical technique for constructing Mohr’s fracture hypothesis-based criteria. The polynomial expansion is then truncated at the quadratic terms to approximately describe the failure function. Besides the basic strengths of UD laminates, the fracture plane angles under transverse tension/compression and pure shear are introduced to calibrate the failure criteria, since Mohr’s concept can be described completely and exactly only by both the basic strengths and the fracture plane angles. According to experimental evidences, the interaction between matrix-dominated and fibre-dominated failure modes is also considered in the present study. No empirical or artificially defined parameters are included in the criteria. Experimental verification for different kinds of unidirectional composites under various stress states demonstrates that the proposed failure criteria have a good predictive ability.
  • Influence of fibre orientation on pultruded GFRP material properties
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Shaohua Zhang, Colin Caprani, Amin Heidarpour Pultruded glass fibre reinforced polymer (GFRP) has light weight, good strength, and excellent resistance to corrosion. These features make GFRP a material well-suited for civil engineering applications. Considering the composite action of fibre and resin in pultruded GFRP, understanding the dependency of strength and stiffness on its material constituents has gained interest amongst researchers. This paper studies the influence of fibre orientation on material properties of pultruded GFRP, namely tensile strength and elastic modulus. Eighty coupons with fibre orientations from 0° to 90° are tested under uniaxial tensile loadings. Based on the experimental results, a generalized Hankinson’s formula is proposed to predict the off-axis properties of pultruded GFRP. To verify this proposed formula, off-axis strengths and elastic moduli of pultruded GFRP from previous studies are compared with the predictions. This work should find use in structural design guidelines for pultruded GFRP, and provides a complete understanding of fibre orientation effect.
  • An efficient bionic topology optimization method for transversely
           isotropic materials
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Harald Völkl, Daniel Klein, Michael Franz, Sandro Wartzack Optimization specifically for fiber reinforced plastics (FRP) is becoming more and more important for creating high-quality composite structures. Yet, in spite of the increasing use of topology optimization (TO) within product development, specific TO methods for transversely isotropic materials like FRP are scarce in research and even more scarce in practical application. This is amongst other reasons caused by the challenge of simultaneous optimization of mutually dependent material distribution and fiber orientations, which poses an obstacle to established gradient-based optimization routines in terms of iterations (run time) and gradient formulation. Thus, based on bionic methods, an efficient, empirical optimization method is proposed to enable fast and FRP-suitable geometry propositions. Case studies show efficiency and effectiveness: the new approach offers very fast convergence; plus perceptible stiffness gains compared to established topology optimization for isotropic materials.
  • Design approach for flexural capacity of concrete T-beams with bonded
           prestressed and nonprestressed FRP reinforcements
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Fei Peng, Weichen Xue Concrete beams with prestressed and nonprestressed fiber-reinforced polymer (FRP) reinforcements are commonly employed in field applications. However, available flexural strength design approaches mainly focus on rectangular concrete beams exclusively prestressed with FRP tendons. This paper, therefore, presents a simplified yet rational design approach for flexural capacity of concrete T-beams with bonded prestressed and nonprestressed FRP reinforcements. Firstly, a new transition region between tension- and compression- controlled sections was proposed in terms of ratio of provided-to-balanced reinforcement (ρe,b 
  • Experimental and numerical analyses of matrix shrinkage and compressive
           behavior of 3-D braided composite under thermo-oxidative ageing conditions
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Man Zhang, Baozhong Sun, Bohong Gu Matrix shrinkage induced in thermo-oxidative ageing process of composites may lead to interfacial damage and thus significantly affect their mechanical properties. This work aims to characterize the oxidation-induced matrix shrinkage in three-dimensional (3-D) braided composite. Specimens were exposed at hot air (180 °C) for 4, 8, and 16 days respectively. Interferometric microscope was employed to determine the matrix shrinkage in composite surface under different ageing conditions. The resulting interfacial damage was observed by optical microscopic examination. Based on the experimental results, we propose a two-step numerical methodology to investigate the effect of thermo-oxidative ageing on compressive properties of braided composite. The established finite element model can effectively capture the deformed and degraded configuration of the aged material. Further simulation results reveal that the shrinkage-induced interfacial damage leads to a lower stress distribution in the exposed ends of braiding yarns. The ultimate deterioration in compressive properties of braided composite is attributed to both resin degradation and yarn-matrix interfacial damage.
  • Joining of thermoplastic structures by Friction Riveting: A mechanical and
           a microstructural investigation on pure and glass reinforced polyamide
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): F. Gagliardi, R. Conte, C. Ciancio, G. Simeoli, V. Pagliarulo, G. Ambrogio, P. Russo Friction Riveting is a spot joining, which consists in rotating a cylindrical rivet and inserting it into clamped sheets. In the first friction phase, the rotational speed and the applied axial force heat the material by friction plasticizing it. After that, the spindle rotation is stopped and the axial force is increased passing to the so called forging phase. Several working parameters, such as the rotational speed, the friction and forging times, and the friction and forging pressure, have to be optimized to achieve sound connections.In the proposed work, the attention was given to the joints of sheets made of a thermoplastic material with and without short glass fiber reinforcements. Rivets were made of Titanium Grade 2. The quality of the obtained results was verified by tensile tests. Moreover, microscopic observations were performed analyzing the material deformation and integrity inside the connection volume. The influences of the monitored process parameters on the above highlighted outputs were reported providing a guideline for the process execution.
  • Reliability-based design optimization of composite battery box based on
           modified particle swarm optimization algorithm
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Zhao Liu, Chao Zhu, Ping Zhu, Wei Chen The application of carbon fiber reinforced polymer (CFRP) material introduces great challenges to the optimization design process, such as complex non-linear material behavior, the inherent uncertainty of design variables and multilevel characteristics of the structure. This paper aims at developing a reliability-based design optimization (RBDO) method to solve the CFRP battery box lightweight design problem considering both meso- and macro-scopic parameters. The method has three kernel parts: the uncertainty quantification and propagation part, the finite element analysis part and the optimization part. In the first part, the internal geometry variability of plain woven CFRP was obtained by X-ray micro-CT images. Representative Volume Element (RVE) models are established to predict the elastic and strength properties of the studied composites, and the constitutive model of material was adapted in stiffness and strength analysis of the battery box structure in the second part. Then a RBDO procedure considering design variables across two scales is developed using a modified particle swarm optimization and surrogate modeling techniques. The structure of the CFRP battery box achieved by the proposed multiscale optimization procedure realizes a weight loss of 22.14%, and the performance demands are satisfied with high reliability, which further reveals the advantages of using this methodology.
  • A methodology to simulate low velocity impact and compression after impact
           in large composite stiffened panels
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): A. Soto, E.V. González, P. Maimí, J.A. Mayugo, P.R. Pasquali, P.P. Camanho Low velocity impact events significantly reduce the mechanical performance of composite structures even though the damage might be barely visible. Numerical simulations can be used to understand and improve the damage resistance and tolerance of composite structures. However, numerical simulations are usually computationally intensive and their application in large composite structures is limited. Furthermore, the numerical models require many parameters that affect their efficiency, accuracy, objectivity and robustness. The present work describes a methodology to simulate low velocity impact and compression after impact which is applied to a composite stiffened panel undergoing visible impact damage. The key definitions are discussed and special attention is devoted to the computational efficiency. The numerical results are compared with experimental data, and the suitability of the proposed methodology is discussed.
  • Elastic buckling of a cylindrical panel with symmetrically varying
           mechanical properties – Analytical study
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Krzysztof Magnucki The subject of the paper is a cylindrical panel with symmetrically varying mechanical properties in the thickness direction. The nonlinear hypothesis of deformation of the straight line normal to the panel neutral surface is assumed. Based on the principle of stationary potential energy differential equations of equilibrium are obtained. The system of the equations is analytically solved and the critical loads of cylindrical panel are derived. Moreover, a simplified model of the cylindrical panel without shear effect is formulated. The results of critical loads for example structures are calculated and presented in Tables.
  • Determination and modeling of bending properties for continuous fiber
           reinforced C/C-SiC sandwich structure with grid core
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Yuan Shi, Pranav Kumar Dileep, Bernhard Heidenreich, Dietmar Koch The sandwich structures based on continuous fiber reinforced grid cores and skin panels have been developed via Liquid Silicon Infiltration (LSI) and in situ joining methods. Because of its excellent specific stiffness and temperature resistance, these lightweight structures have a sound potential for various application areas such as aerospace and construction industries. In this study, the characterization of the mechanical performance of grid core structures for continuous fiber reinforced C/C-SiC sandwich composites under four-point-bending load is presented. The effective bending and shear stiffness and the deflection at mid-span of the sandwich structure are determined and compared through experimental, analytical and FE-simulation (Finite Element simulation) approaches. The comparison showed good correlation. The analytical and FE-simulation approaches have been further used to study the parameter effects and the influence of the different grid core structures on the bending properties respectively. The proposed different approaches are suitable to determine and simulate the mechanical properties of C/C-SiC sandwich structures and are versatile tools for further product development.
  • Identification of the elastic constant values for numerical simulation of
           high velocity impact on dyneema® woven fabrics using orthogonal
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Zishun Yuan, Xiaogang Chen, Haoxian Zeng, Kaicheng Wang, Jiawen Qiu Dyneema® fibres and fabrics are widely used for ballistic protection due to its lightweight and super mechanical properties against high strain rate impact, and finite element (FE) simulation and analysis are used to study the response to the impact in parallel to the experimental-based research methods. However, elastic constants of the yarn except the Young’s modulus were difficult to obtain and were basically assigned based on assumptions and approximations in the FE modelling, which caused some inaccuracies. This paper reports a study on the influence of each elastic constant of Dyneema® yarn model in modelling a single layer Dyneema® woven fabric against ballistic impact using the orthogonal experiment method. Orthogonal table L25 (56) was employed to analyse six factors (i.e. E11, E33, ν, G13, G23, and their interactions) with each having five levels. The ballistic modelling results were validated against the experimental results, viz. energy absorption, failure time of the first yarn broken and number of failed yarns. According to the orthogonal analysis, G13 was shown as the most significant in influencing the simulated results, with a confidence level of more than 95%, and ν was the least significant. Through the orthogonal study, the combination of levels of the elastic constants that led to a significant agreement between the FE and practical results was identified.
  • A new higher order shear deformation theory for static, vibration and
           buckling responses of laminated plates with the isogeometric analysis
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Peng Shi, Chunying Dong, Fuzhao Sun, Wenfu Liu, Qiankun Hu A new hyperbolic tangent shear deformation theory (HTSDT) for the static, free vibration and buckling analysis of laminated composite plates is presented. In the present theory, shear stresses disappear at the top and bottom surfaces of the plates and shear correction factors are no longer required. Weak forms of the static, free vibration and buckling analysis for laminated composite plates based on the HTSDT are then derived and are numerically solved using the isogeometric analysis (IGA). The proposed formulation requires C1 continuity generalized displacements, whereas the basis functions used in IGA can perfectly fulfill this requirement. Based on the available solutions in the literature, the present method shows high accuracy and efficiency when numerical examples are solved.
  • Delamination detection in composite laminates using low frequency guided
           waves: Numerical simulations
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): Siavash Shoja, Viktor Berbyuk, Anders Boström The aim of this study is to find an efficient way of finite element modelling of guided wave propagation in composite laminates to detect delaminations. A novel approach is proposed to model delaminations by locally reducing the stiffness and it is implemented in a finite element shell model. The approach is verified by comparing the results with the results of two existing approaches. Results show that the stiffness reduction approach gives reasonable accuracy for the primary wave modes and improvement in simulation time. Moreover, it is shown that new convergence criteria should be considered to simulate the guided wave propagation. Additionally, the Pearson correlation coefficient is introduced as a good criterion for delamination detection in such problems. All the conclusions are made when simulations are performed in the low frequency range and can be used to study guided wave propagation in large composite structures such as wind turbine blades.
  • Experimental study on ultra-high ductility cementitious composites applied
           to link slabs for jointless bridge decks
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Mengjun Hou, Kexu Hu, Jiangtao Yu, Siwei Dong, Shilang Xu As a member in the engineered cementitious composites (ECC) family, ultra-high ductility cementitious composites (UHDCC) has the tensile strain capacity ranging from 6% to 12%. The present study aims to investigate the effect of UHDCC on the performance of link slabs for jointless bridge decks subjected to fatigue loading. To explore the fatigue durability of UHDCC, fatigue bending tests were carried out on six plain UHDCC beams at different stress levels. UHDCC exhibited multi-cracking, strain-hardening characteristics and satisfying fatigue durability at high load levels. A fitting equation was proposed to summarize the relation between stress level and fatigue life. Furthermore, three full-scale jointless bridge decks were tested to failure under fatigue loading. Two specimens made of steel reinforced UHDCC exhibited superior fatigue durability to that made of steel reinforced concrete, even if they experienced much larger deformation and steel strain. The test results indicated that the presence of UHDCC can effectively alleviate the strain fluctuation range of steel, reduce the input energy intensity, and improve the energy dissipation capacity of specimens, thus enhancing the fatigue life of steel bars. The findings above were demonstrated by a further analysis on the cumulative dissipated energy in the final part of the article.
  • Experimental and numerical assessment of aerospace grade composites based
           on high-velocity impact experiments
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Tim Wagner, Sebastian Heimbs, Florian Franke, Uli Burger, Peter Middendorf The experimental and numerical assessment of different aerospace grade composite materials under high-velocity impact is treated in this study. Characterisation of the materials, including thermosets (epoxy) and thermoplastics (PEEK) with carbon (unidirectional and woven fabric) and glass fibres, was conducted using high-velocity impact experiments. The test results indicate the glass fibre composites’ superiority in the domain of classical composites in terms of weight-specific impact performance. The different carbon fibre composites have very similar ballistic limits but differ in terms of delamination behaviour. Subsequently, materials models are developed which reproduce interlaminar failure through the usage of surface-based cohesive contact formulations. By these means efficient and reliable simulation methods for impact events are developed.
  • Damage Accumulation in Braided Textiles-reinforced Composites under
           Repeated Impacts: Experimental and Numerical Studies
    • Abstract: Publication date: Available online 29 July 2018Source: Composite StructuresAuthor(s): Chen Wang, Zhong Chen, Vadim V. Silberschmidt, Anish Roy Composites reinforced with braided textiles exhibit high structural stability and excellent damage tolerance, making them very attractive for defence, aerospace, automotive and energy industries. Considering the real-life service environment, it is crucial to study a dynamic response of a composite structure and its energy-dissipation ability, especially under repeated low-velocity impacts. So, a series of drop-weight tests were carried out followed by X-ray computed micro-tomography to characterize damage morphology of braided composite specimens. Meanwhile, a multi-scale computational approach was explored and implemented as a user-defined-material subroutine (VUMAT) for ABAQUS/Explicit to capture main damage modes of a braided textile composite, while its delamination was modelled by employing cohesive-zone elements. Load- and energy-time curves were obtained both experimentally and numerically. The predicted levels of peak forces and absorbed energy were found to agree with the experimental data. An extent of delamination and damage accumulation in the braided composite was predicted numerically and analysed; it was found that material responses to repeated impacts had two types depending on the level of normalised impact energy. The presented modelling capability could contribute to design of braided composite structures for various applications.
  • Spectroscopic Evaluation of Structural Changes in Composite Materials
           Subjected to Self-Heating Effect
    • Abstract: Publication date: Available online 29 July 2018Source: Composite StructuresAuthor(s): Roman Turczyn, Katarzyna Krukiewicz, Andrzej Katunin Due to their excellent mechanical properties and low weight, polymer composites have gained a lot of attraction as materials for numerous engineering applications. Many of these machine components are, however, subjected to intensive loading and vibrations, which may lead to the occurrence of a self-heating effect. This can further enhance the fatigue process and result in the significant intensification of structural degradation, e.g. matrix and interface cracks, as well as delamination. The self-heating effect should be, therefore, considered as a serious concern wherever the polymer composite elements are applied. In our study, we focus on the extensive evaluation of the consequences of self-heating effect for the structural and chemical degradation of polymer composite materials. Microscopic and spectroscopic techniques are applied to evaluate the results of self-heating effect on the series of glass fiber reinforced polymer specimens subjected to cyclic mechanical loading. As the result, we provide the range of self-heating temperature values, for which the beneficial residual cross-linking reactions dominate over the concurrent thermal degradation processes.
  • Nonlinear bending, buckling and vibration of bi-directional functionally
           graded nanobeams
    • Abstract: Publication date: Available online 29 July 2018Source: Composite StructuresAuthor(s): Tianzhi Yang, Ye Tang, Qian Li, Xiao-Dong Yang In this paper, a new nonlinear model of nanobeams made of bi-directional (2D) functionally graded material (FGM) is presented. The material properties are assumed to obey an exponential gradation along both the thickness and length directions. The equation of motion is derived based on Euler-Bernoulli beam theory, von Kármán geometric nonlinearity and non-local elasticity theory. The nonlinear bending, buckling and vibration of the nanobeams with size effect is investigated. Results show that the 2D FGM introduces an additional stiffness term in governing equation, so it cannot be solved by classical analytical methods. Therefore, the differential quadrature method (DQM) is used to solve the nonlinear problem. The size-dependent nonlinear critical load and frequencies are calculated. The effect of different material parameters, boundary conditions and size scale are discussed in details.
  • Isogeometric Analysis of functionally graded porous plates reinforced by
           graphene platelets
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Keyan Li, Di Wu, Xiaojun Chen, Jin Cheng, Zhenyu Liu, Wei Gao, Muyu Liu This paper investigates the static linear elasticity, natural frequency, and buckling behaviour of functionally graded porous plates reinforced by graphene platelets (GPLs). Both first- and third-order shear deformation plate theories are incorporated within the Isogeometric Analysis (IGA) framework. The pores and the GPLs within the plates are distributed in the metal matrix either uniformly or non-uniformly according to different patterns. The graded distributions of porosity and nanocomposite are achieved by material parameters varying across the thickness direction of plate. The Halpin-Tsai micromechanics model is implemented to establish the relationship between porosity coefficient and Young’s modulus, as well as to obtain the mass density of the nanocomposite. The variation of Poisson’s ratio is determined by the mechanical properties of closed-cell cellular solids under Gaussian Random Field scheme. A comprehensive parametric study is accomplished to investigate the effects of weight fraction, distribution pattern, geometry, and size of the GPLs reinforcement on the static linear elasticity, natural frequency, and buckling behaviour of the nanocomposite plates with diverse metal matrices and porosity coefficients. The outcome of numerical investigation shows that the inclusion of the GPLs can effectively improve the stiffness of functionally graded porous plate.
  • The MLPG for crack analyses in composites with flexoelectricity effects
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Jan Sladek, Vladimir Sladek, Milan Jus The meshless Petrov-Galerkin (MLPG) method is developed to analyse 2-D crack problems where the electric field and displacement gradients exhibit a size effect. The size-effect phenomenon in micro/nano electronic structures is described by the strain- and electric field-gradients. Both the electric intensity vector and strain gradients are considered in the constitutive equations of the material and the governing equations are derived with the corresponding boundary conditions using the variational principle. The coupled governing partial differential equations (PDE) for stresses and electric displacement field are satisfied in a local weak-form on small fictitious subdomains. All field quantities are approximated by the moving least-squares (MLS) scheme. After performing the spatial integrations, we obtain a system of algebraic equations for the nodal unknowns.
  • Buckling of symmetrical circular sandwich plates with variable mechanical
           properties of the core in the radial direction
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): E. Magnucka-Blandzi, K. Wiśniewska-Mleczko, M.J. Smyczyński The study is devoted to thin-walled clamped symmetrical three-layer circular plate. The sandwich plate consists of two facings, and a metal foam core. The mechanical properties of the core plate vary along its radius, remaining constant in the facings. The main goal of the study is to elaborate a mathematical model of the compressed circular plate in its middle plane, analytical description and solution of the global buckling problem. The nonlinear hypothesis of deformation of the normal to the middle plane of the plate is formulated. The equations of equilibrium are derived based on the principle of stationary total potential energy. The proposed mathematical model of the displacements considers the shear effect. The analytical model is verified numerically with the use of Finite Element Analysis.
  • Free vibration characteristic of laminated conical shells based on
           higher-order shear deformation theory
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Saira Javed The purpose of this research is to analyse the free vibration of composite laminated conical shells based on higher order shear deformation theory. The vibrational behavior of multi-layered conical shells are analyzed for simply supported end condition. The coupled differential equations in terms displacement and rotational functions are obtained. These displacement and rotational functions are invariantly approximated using cubic and quantic spline. A generalized eigenvalue problem is obtained and solved numerically for an eigenfrequency parameter and an associated eigenvector of spline coefficients. The different materials are used to show the parametric effects of shell’s length ratio, cone angle, stacking sequence and number of lamina on the frequency of the conical shells. The numerical results obtained using spline approximation are validated through existing literature.
  • Vibration and flutter analysis of supersonic porous functionally graded
           material plates with temperature gradient and resting on elastic
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Kai Zhou, Xiuchang Huang, Jiajin Tian, Hongxing Hua In this paper, a unified solution is developed to analyze the vibration and flutter behaviors of supersonic porous functionally graded material (FGM) plates with general boundary conditions, in which the classical and non-classical boundary conditions can be dealt with. The one-dimensional Fourier equation of heat conduction is employed to calculate the temperature distribution through the thickness direction of the plate and the properties of temperature dependent materials can be further obtained. The first-order shear deformation theory (FSDT) and supersonic piston theory considering the yawed flow angle effect are employed to formulate the strain energy, kinetic energy and external work functions of the system. The motion equations of the supersonic porous FGM plate are derived by using the Hamilton’s principle and the displacement components of the plate are expanded by the Fourier series combined with auxiliary functions. A considerable number of numerical examples concerning the vibration and flutter of the supersonic porous FGM plate are carried out to show the accuracy and efficiency of the described method. Finally, the effects of the boundary condition, material property distribution, elastic foundation, temperature field, porosity volume fraction and yawed flow angle on the flutter characteristics of the supersonic FGM plate are analyzed in detail.
  • Behavior of Shear Thickening Fluid (STF) impregnated fabric composite rear
           wall under hypervelocity impact
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): YunHo Kim, Yurim Park, JiHun Cha, Venkat Akhil Ankem, Chun-Gon Kim On the contrary to previous researches on Shear Thickening Fluid (STF) impregnated fabric composites as a protection method against low to middle velocity impact such as stabbing or bulletproofing, the application of STF on space shields seems to be quite skeptical due to high-speed range of micro meteoroid and orbital debris (M/OD). However, the results of the eight types of fabric rear layers involving STF impregnated fabric of this study suggest that STF impregnated fabric can be a promising candidate for the improved rear wall of a space shield. After hypervelocity impact to the Al 6061-T6 frontal bumper, the all Heracron fabric rear wall was not fully penetrated against the hypervelocity fragments. However, a large hole was found in case of 2 mm Al 6061-T6 rear wall with the almost identical areal density and impact velocity. By replacing last 10 Heracron fabric layers from the rear side of the fabric rear wall to 6 layers of STF impregnated fabric, the trend in the number of undamaged layers was positively inversed. The study shows experimentally that the fabric rear wall of a space shielding system can be enhanced effectively by using STF impregnated layers.
  • Size effects in elastic-plastic functionally graded materials
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Tittu V. Mathew, Sundararajan Natarajan, Emilio Martínez-Pañeda We develop a strain gradient plasticity formulation for composite materials with spatially varying volume fractions to characterize size effects in functionally graded materials (FGMs). The model is grounded on the mechanism-based strain gradient plasticity theory and effective properties are determined by means of a linear homogenization scheme. Several paradigmatic boundary value problems are numerically investigated to gain insight into the strengthening effects associated with plastic strain gradients and geometrically necessary dislocations (GNDs). The analysis of bending in micro-size functionally graded foils shows a notably stiffer response with diminishing thickness. Micro-hardness measurements from indentation reveal a significant increase with decreasing indenter size. And large dislocation densities in the vicinity of a crack substantially elevate stresses in cracked FGM components. We comprehensively assess the influence of the length scale parameter and material gradation profile to accurately characterize the micro-scale response and identify regimes of GNDs relevance in FGMs.
  • Exact solution for size-dependent elastic response in laminated beams
           considering generalized first strain gradient elasticity
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Sai Sidhardh, M.C. Ray In this paper, exact solutions for the static bending response of laminated composite beams have been derived considering the effect of strain gradient elasticity. Separate solutions for the laminate comprising of isotropic and orthotropic laminae have been presented here. The sixth-order tensor for the higher order elastic coefficients has been evaluated using the generalized first strain gradient elasticity model with three independent material length constants. The significance of the gradient elasticity in low-dimensional structures has been established employing numerical examples of micro and nano-beams, and comparing the current results with the classical elasticity results. A parametric study over the variation of the axial, transverse Cauchy and physical stresses across the thickness of the beam has been conducted. Also, the discontinuity of the inter-laminar transverse Cauchy stresses and higher order stresses across the thickness has been studied in the current framework. The exact solutions developed in this paper may be used as benchmark results for validating further research involving the strain gradient elastic response of low-dimensional laminated composite beams.
  • Research on the dynamic mechanical properties of polymethacrylimide foam
           sandwich structure
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Jia Qu, Dianwei Ju, Shenrou Gao, Jiawei Chen Polymethacrylimide foam is fully closed-cell isotropic foam which possesses high stiffness and strength to weight ratios. The paper reports the findings of an experimental study developing to investigate the quasi-static and dynamic response of sandwich panels based on polymethacrylimide foam using compression tests and Split Hopkinson Pressure Bar, respectively. The effect of thickness of aluminum face sheet, thickness and density of the polymethacrylimide core on the mechanical properties of the sandwich structures are studied respectively. It is shown that core density has the greatest effect on compressive strength of sandwich structure. The elasticity modulus and compressive strength of sandwich decreased by 40% under quasi-static compressive when the density of the core reduced by 28%. Secondly, dynamic compressive experiment results show that when the density of the core reduced by 28%, at the strain rate of 150 s−1, compressive strength decreased by 45%; strain rate 310 s−1, compressive strength reduced by 42%. When the strain rate increased from 7.6 × 10−4 s−1 to 150 s−1, compressive strength increased by 26%; strain rate increases from 7.6 × 10−4 s−1 to 310 s−1, compressive strength increased by 43%. The dynamic mechanical properties of polymethacrylimide foam sandwich panels accompanied with the increase of strain rate. Finally, dynamic constitutive relation of Cowper-Symonds function is fitted.
  • Process-induced residual stress of variable-stiffness composite laminates
           during cure
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Guiming Zhang, Jihui Wang, Aiqing Ni, Shuxin Li One of the most important issues for designing variable-stiffness composite structures reflects on determination of the steered fiber paths. In this paper a linear variation of steered fiber curves and the change rule of the fiber angles were presented to create the mathematical model of variable-stiffness composite laminates. Compared to the straight-fiber laminate, the reference path with linearly changed angles leads to higher mechanical strength and more design freedoms. A novel methodology was developed to predict the distributions of process-induced residual stresses during cure. A three-dimensional (3D) thermochemical model of the curing process was established and the mechanical responses during cure were evaluated coupled with the results of thermochemical analyses. The distributions of the temperature and the degree of cure were obtained. The process-induced residual stresses were calculated using ABAQUS. The resin modulus was determined using the cure hardening instantaneous linear elastic (CHILE) model. The cure kinetic process was simulated using Kamal model for AS4/3501-6 prepregs. The results show that the process-induced residual stresses of variable-stiffness composite panels are reduced with increasing the end angle of the present fiber path during cure.
  • Clustering effect on damage mechanisms in open-hole laminated carbon/epoxy
           composite under constant tensile loading rate, using acoustic emission
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): Hassan Sayar, Mohammad Azadi, Ahmad Ghasemi-Ghalebahman, Seyed Mohammad Jafari In the present research, damage mechanisms in the open-hole laminated carbon/epoxy composite have been investigated using the acoustic emission method. For such objective, standard specimens, made of the pure resin, the pure fiber and composites, were tested under tensile conditions, at a constant loading rate. Then, the clustering effect was studied in order to know which damages (debonding, fiber pull-out, delamination, matrix cracking and fiber breakage defects) occurred in the material. For the analysis of acoustic emission signals, wavelet packet transform and fuzzy C-means methods were applied to data. Obtained results indicated that the frequency range for matrix cracking, the fiber breakage, the fiber pull-out, debonding of fibers from the matrix and the delamination was obtained as 100–250 kHz, 420–500 kHz, 250–320 kHz, 320–380 kHz and 380–420 kHz, respectively. Scanning electron microscopy images showed that the dominant damage was qualitatively related to debonding, the fiber pull-out and the delamination, which had a proper agreement with obtained results from the analysis of acoustic emission signals.
  • Strain rate effects on the compressive response of wood and energy
           absorption capabilities – Part B: Experimental investigation under rigid
           lateral confinement
    • Abstract: Publication date: 15 November 2018Source: Composite Structures, Volume 204Author(s): J. Wouts, G. Haugou, M. Oudjene, H. Morvan, D. Coutellier The compressive properties of spruce and beech wood species at a large range of strain rates – from 0.001 to 600 s-1 – under rigid lateral confinement have been investigated, using an original experimental device especially developed for the purpose. The work is motivated by the need to explore the dynamic behavior of wood up to large strains close to 70%. Three experimental apparatus have been used to obtain the compressive responses: the quasi-static tests have been performed using a Sintech 20D test system, the compressive responses at intermediate strain rates have been obtained with an Instron VHS65/20 apparatus and the dynamic tests have been conducted using a Split Hopkinson Pressure Bars (SHPB) system. The strain rate sensitivity of wood is clearly visible on the crushing strength with an increase between 80 and 155% but also on the plastic like behavior. In addition, the entire responses exhibit an elastic-plastic like behavior whereas an elastic brittle behavior could be observed, in the previous Part A which was focused on the compression configuration without lateral confinement. Even if no significant effect of the rigid lateral confinement is observed on the apparent Young modulus and the crushing strength values for both species, the wood energy absorption capability is better when longitudinal failure mechanisms are restricted thanks to the rigid lateral confinement.
  • Towards an understanding of variations in the buckling of tailored
           variable angle tow composite plates
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): Xiao-Yi Zhou, P.D. Gosling In this paper, variable angle tow (VAT) composite plates tailored to enhance buckling performance are studied with the use of stochastic finite element method to quantify uncertainties in buckling measures arising from variations in material properties and fibre tow path. Detailed formulations for predicting buckling statistics in terms of mean value and standard deviation are derived to enable a perturbation-based stochastic finite element analysis. The derivations are built on a linear variation formula for fibre tow path and plate element based on the first order shear deformation theory. They are integrated with Taylor series expansion to propagate uncertainties from inputs to buckling performance measures, including buckling eigenvalues, critical buckling coefficients, etc. A twelve-layer VAT composite plate, with optimally designed fibre tow paths under various boundary conditions, has been investigated to illustrate the uncertainty quantification procedure. The performance of the perturbation-based stochastic finite element method has been validated using Monte Carlo simulation. Influences of variations in material properties and fibre tow path are thoroughly examined to understand the variability of buckling performance of VAT composites.
  • Post-buckling behaviour and delamination growth characteristics of
           delaminated composite plates
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): Anton Köllner, Christina Völlmecke The problem of a delaminated composite plate subjected to in-plane compressive loading is investigated by employing a novel analytical framework previously developed by the authors. The framework is capable of modelling the post-buckling behaviour considering damage growth by using a set of generalized coordinates only. Therefore, in order to model the post-buckling responses of delaminated composite plates a Rayleigh–Ritz formulation is employed. Thus, the post-buckling behaviour as well as the delamination growth characteristics are determined by solving a set of non-linear algebraic equations only. For the cases investigated, the study reveals that delamination growth is associated with the global buckling response. So long as stable delamination growth is present, the post-buckling response remains also stable. However, unstable delamination growth may be caused which would occur unexpectedly yielding sudden failure of the structure. This underlines the importance of considering delamination growth when studying the structural stability behaviour of these structures.
  • Analytical model of functionally graded material/shape memory alloy
           composite cantilever beam under bending
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): N.V. Viet, W. Zaki, R. Umer A new analytical model for a functionally graded material (FGM)/shape memory alloy (SMA) laminated composite cantilever beam subjected to a concentrated tip load is developed. The novelty of this work lays in the analytical modelling of moment-curvature and shear force-shear strain relations, which are derived based on ZM model and Timoshenko’s theory for all stages during loading and unloading. A high-accuracy numerical solution and a three-dimensional finite element analysis (3D FEA) for the composite beam are carried out to validate the analytical solution. The results show very good agreement in each case. The influence of gradient direction, gradient index, temperature, and relative thickness ratio of SMA to functionally graded layer on superelasticity of carbon nanotube (CNT)-epoxy-based-FGM/SMA composite beam is also examined. The results show that the superelasticity of CNT-epoxy FGM/SMA composites increased with an increase in gradient index and decreased with an increase in thickness ratio. The temperature variations induced less effect on the superelasticity of FGM/SMA composites. Furthermore the composite beam with FGM layers having the Young’s modulus graded increasingly in the inward direction exhibits a better superelastic property in comparison with that with FGM layers having the Young’s modulus graded increasingly along the outward direction.
  • Multiscale analysis of nonlinear composites via a mixed reduced order
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): F. Covezzi, S. de Miranda, S. Marfia, E. Sacco In this paper a new multiscale approach is presented for the analysis of structures made of composite material characterized by elastoplastic or viscoplastic nonlinear response. Scale separation is assumed so that the homogenization theory can be applied: at the structural scale (macroscale) the material appears as homogeneous, while at the microscale it is characterized by a heterogeneous microstructure that affects the global behavior of the structure. The resolution of the micromechanical problem is performed developing a reduced order homogenization technique based on a mixed variational formulation, named Mixed Transformation Field Analysis (MxTFA). The microscopic reduced internal variables are the stress and plastic multiplier parameters of RVE subsets, whose evolution is computed enforcing the weak form of the governing equations for every subset. Some numerical tests are performed to show the accuracy and efficiency of the proposed multiscale technique.
  • Mechanical properties of agglomerated cork stoppers for sparkling wines:
           Influence of adhesive and cork particle size
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): Kevin Crouvisier-Urion, Jean-Pierre Bellat, Régis D. Gougeon, Thomas Karbowiak The mechanics of agglomerated cork is a key issue for application to sparkling wine stoppers. Industrial samples were produced by varying the chemical nature of polyurethane adhesives (aliphatic and aromatic), the adhesive concentration and the size of the cork particles (macro and microagglomerated). Uniaxial compression and traction were performed to fully understand the material behavior when submitted to stress. It is noteworthy that agglomerated cork is less rigid than natural cork. This implies that the agglomeration process increases the material elasticity. Moreover, this elasticity is mainly driven by the chemical nature of the adhesive, in the case of macroagglomerated cork. However, it appears that the use of smaller particle sizes (
  • Dynamic compression response of self-reinforced polypropylene composite
           structures fabricated through ex-situ consolidation process
    • Abstract: Publication date: Available online 27 July 2018Source: Composite StructuresAuthor(s): Ali Imran, Shijie Qi, Chun Yan, Dong Liu, Yingdan Zhu, Guilin Yang In case of Self-reinforced polymer composites (SRCs) the fibres and matrix belong to the same family of polymers that can ensure 100% recyclability as compared to traditional fibre reinforced epoxy matrix based composites. Most of the SRCs were studied only on material bases not structural bases, although some structures were fabricated but most of their fabrication methods can hardly be applied for mass production. We fabricated self-reinforced polypropylene (SrPP) structures by ex-situ consolidation process that can be potentially applied for mass production. Instead of conventional stamping process that involves complex formability phenomenon; a mould was designed to fabricate corrugated core from the pre-consolidated SrPP sheets and then face sheets were joined by same family of polymer adhesives to achieve maximum recyclability. Optimal bending temperature was investigated to maintain proper fibre matrix contents of corrugated SrPP sheets. Interface between core and face sheet (FS) was enhanced through phenomenon of mechanical lock by creating various abrasion levels. Dynamic strengthening effect and collapse behaviour of structures during out of plane dynamic compression tests was investigated and compared with theoretical predictions.Graphical abstractGraphical abstract for this article
  • Nonlinear in-plane instability of functionally graded multilayer graphene
           reinforced composite shallow arches
    • Abstract: Publication date: Available online 27 July 2018Source: Composite StructuresAuthor(s): Zhicheng Yang, Jie Yang, Airong Liu, Jiyang Fu This paper investigates the in-plane instability of functionally graded multilayer composite shallow arches reinforced with a low content of graphene platelets (GPLs) under a central point load. The GPL weight fraction, which is a constant within each individual GPL reinforced composite (GPLRC) layer, follows a layer-wise variation along the thickness direction. The effective Young’ modulus of the GPLRC is estimated by modified Halpin-Tsai micromechanics model. The virtual work principle is used to establish the nonlinear equilibrium equations for the FG-GPLRC arch fixed or pinned at both ends which are then solved analytically. A parametric study is conducted to examine the effects of distribution pattern, weight fraction, and size of GPL nanofillers and the geometrical parameters of the FG-GPLRC arch on its buckling and postbuckling behaviors. The conditions for multiple limit point buckling to occur in an FG-GPLRC pinned arch are also discussed. It is found that GPL nanofillers have a remarkable reinforcing effect on buckling and postbuckling performances of nanocomposite shallow arches.
  • Static and dynamic bearing failure of carbon/epoxy composite joints
    • Abstract: Publication date: Available online 21 July 2018Source: Composite StructuresAuthor(s): Gérald Portemont, Julien Berthe, Alain Deudon, François-Xavier Irisarri Mechanical fastening is a common method used to join composite materials in aeronautical industry. Various studies have been performed dedicated to the behaviour of composite bolted joints under quasi-static loadings, but only few studies deal with the dynamic behaviour (crash or impacts). The aim of this work is to study the loading rate influence on the bearing response of a carbon/epoxy laminate loaded by a pin. For that purpose, a double shear test fixture has been specially designed to measure the global behaviour and the local response around the pin. Infrared thermography and Digital Image Correlation techniques have been used to detect, map and characterize dissipative phenomena evolution. The tests have been performed on a servo-hydraulic jack with a loading rate ranging from 10-4 m/s to 1 m/s. An increase of the peak bearing load of more than 20% is observed with the loading rate increase. A decrease of the load plateau of more than 60% is obtained. Simultaneous measurements of thermal and kinematic fields in this work give access to the evolution of the damage-related dissipative phenomena close to the pin. These dissipative phenomena were found to be significantly dependent on the loading rate.
  • A Micromechanics-Based Processing Model for Predicting Residual Stress in
           Fiber-Reinforced Polymer Matrix Composites
    • Abstract: Publication date: Available online 19 July 2018Source: Composite StructuresAuthor(s): Weijia Chen, Dianyun Zhang An experimentally validated, multi-physics and multi-scale processing model was developed to predict the residual stress buildup in a polymer matrix composite during manufacturing. At the macroscale, the composite was modeled as discrete layers of homogeneous, transversely isotropic laminae, while micromechanics was implemented at the subscale to compute the effective lamina responses based on the fiber and matrix properties through an Extended Concentric Cylinder Assemblage (ECCA) model. The composite temperature and Degree of Cure (DOC) distributions were solved by incorporating resin cure kinetics into heat transfer analysis, which were used in the subsequent stress analysis to determine the cure-dependent composite responses, including cure-dependent modulus, thermal strain, and chemical shrinkage. This integrated processing model was applied to predict the cure-induced warpage of a non-symmetric laminate. The proposed model, which incorporates resin cure kinetics, cure-dependent constitutive law, and tool–part interaction, demonstrates good agreement with the experiment on the prediction of the warpage curvatures.
  • Metal-coated hybrid meso-lattice composites and their mechanical
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): Jian Song, Libo Gao, Ke Cao, Hongti Zhang, Shang Xu, Chenchen Jiang, James Utama Surjadi, Yiming Xu, Yang Lu Developing cellular materials, especially ordered lattice structures, would allow the exploitation of structural advantages and enhance the mechanical performances. However, most lattice structures only consist of a single component material, while less investigations are focus on composite lattices and associated failure mechanisms. Here we fabricated nickel-coated polymer meso-lattice composites (Ni@PMLs) by 3D printing and electroless plating. A quantitative and in situ multi-scale experimental analysis assisted with a high-resolution imaging system was employed. Importantly, a simulation model for the composite was proposed and the damage process was elaborated based on the progressive damage theory and fracture mechanics. These results show that the average modulus and strength of Ni@PMLs can be enhanced by 68.3% and 34.9% respectively, compared to the polymer only lattices (PMLs). Furthermore, the average specific strength of the lattices almost reaches the upper bounds of conventional metal/polymer foams and natural cellular materials, despite that the cascade-shaped beams originating from our 3D printing process may have negative influence on mechanical performance, due to stress concentration and shear-induced failure. The simulated mechanical properties and damage propagation modes agree well with the experimental observations. These findings could be useful for the design/manufacturing optimization and future practical applications of meso-lattice composites.Graphical abstractGraphical abstract for this article
  • Application of complementary optical methods for strain investigation in
           composite high pressure vessel
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): Paweł Gąsior, Marcin Malesa, Jerzy Kaleta, Małgorzata Kujawińska, Krzysztof Malowany, Radosław Rybczyński The work presents the methodology of displacement and strain measurements (in type IV composite high pressure hydrogen and methane storage vessels in areas of the gaseous fuel cell vehicle. The research was conducted in vessels with so called programmed defects in the form of notches and delamination. The complementary optical methods, namely: optical fibre sensing based on Bragg gratings (FBG) and digital image correlation (DIC) method were used for performing local and full-field displacement/strain measurements respectively. It has been shown that DIC can be successfully applied as the method for defect identification in full field of view and that it can support an optimal localization of FBG sensors and their calibration. As FBG sensors are devoted to be integrated with the vessel structure, the proposed methodology constitutes a solution to the difficult problem of building an efficient Structural Health Monitoring (SHM) system for composite high pressure vessels for gaseous fuels. At the same time the measurement data from both systems supports calibration of numerical models of the vessels.
  • Double-layer sandwich annulus with ultra-low thermal expansion
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): Yan Xie, Xu Pei, Jingjun Yu Zero or negative coefficient of thermal expansion (CTE) material is a rare abnormal phenomenon in nature but preferred in such engineering applications as optical components and precision instruments, etc. Most of them in nature are brittle and can operate only in a narrow temperature range. Artificial metamaterials offer a new route towards materials with tunable CTEs and excellent mechanical properties. However, these materials engineered by periodic architectures generally lack homogeneity, and thus the integrations into applications are limited. Here, a double-layer sandwich annulus integrating fork-like lattice cells and continuous interfaces is constructed. As the basis, the tunability of effective CTEs is theoretically modeled to reveal its dependence on the diameters of rings, the lengths of beams with higher CTE in fork-like cells and constituent materials’ CTEs. The thermal properties are also characterized experimentally on a bi-material metallic sample targeting for zero CTE purposely. The measured results demonstrate the ultra-low CTEs (0.54 × 10−6/°C for inner ring and 0.38 × 10−6/°C for outer ring) with a temperature variation of 30–220 °C. Such a double-layer sandwich annulus with tunable CTEs is scale independent and highly promising in high-speed bearings and mirror supports in harsh thermal environments.
  • Low-velocity impact response of carbon fibre composites with novel liquid
           Methylmethacrylate thermoplastic matrix
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): Somen K. Bhudolia, Sunil C. Joshi Experimental investigations were carried out to determine the low-velocity impact behaviour of carbon fibre composites with novel liquid Methylmethacrylate (MMA) thermoplastic matrix, Elium®. The load, deflection and the energy attributes under impact are studied in detail and the baseline comparison is carried with the carbon fibre composites with epoxy matrix. The quasi-isotropic non-crimp carbon fabric (NCCF) laminates were impacted at 25 J, 42 J and 52 J impact energies and the material response of both the composite configurations were studied. The composite laminates have shown less catastrophic damage at a high energy level (52 J) and around 10% higher peak load was observed. Structural integrity as measured from the load-deflection curve demonstrated up to 53% increase for Thin NCCF Elium composite compared to their counterpart composites with epoxy matrix. Significant energy absorption (56%) before the onset of major failure mostly through elastic-plastic deformations was observed for thin NCCF Elium® composite. Impact results at different energies showed the strain sensitivity of Elium® microstructure with the improved performance with increasing impact energy. From the detailed fracture and damage analysis of the impacted samples, the failure mechanisms were deduced for the novel Thin NCCF Elium® and epoxy composites.
  • Cost analysis of variable stiffness composite structures with application
           to a wind turbine blade
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): A. Sohouli, M. Yildiz, A. Suleman This paper presents a design framework for cost analysis of a wind turbine blade made of variable stiffness composite laminates. The framework consists of a design optimization, time-variant reliability analysis, structural performance analysis, and life-cycle cost evaluation phases. The objective of the optimization phase is the maximization of the stiffness by searching the optimum values of the design variables. The design variables are piecewise patch orientations and material properties of the fiber reinforced composites. Different volume constraints of carbon fiber reinforced polymer (CFRP) are imposed on composite laminates in the load-carrying component. Next, the structural performance and the service lifetime of the blade designs are estimated based on the time-variant reliability assessment. The time-variant reliability is evaluated using an outcrossing asymptotic method. The wind speed and the material properties are considered, respectively as the random process and the random parameters during the reliability assessment. The maintenance cost of the blade designs is determined by the combination of the estimated structural performance and an analytical method. Finally, the final designs are selected according to the cost-effectiveness values of the designs under the different discount rates and the undiscounted costs.
  • Structural gradient based sizing optimization of wind turbine blades with
           fixed outer geometry
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): J.H. Sjølund, E. Lund In this work the mass of a 73.5 m offshore wind turbine blade is minimized while considering manufacturing constraints, tip displacement, buckling, and static strength criteria when subject to an extreme load envelope consisting of 12 load directions. The gradient based sizing optimization takes offset in the outer geometry and loading from a commercial 73.5 m wind turbine blade where the manufacturing mold should be re-used and hence the outer geometry is kept constant. A solid-shell finite element model of the full blade is used as basis for the optimization. The blade is divided into patches and thicknesses of ply-groups (groups of contiguous plies with the same material and fiber orientation) are used as design variables. The design variables are assumed continuous in the optimization phase. Sequential linear programming (SLP) is used to solve the problem with semi-analytical gradients. In the post-processing phase the lay-up is refined and ply-group thicknesses are rounded to a whole number of plies. The gradient based sizing optimization results in a reduced mass and many active constraints across multiple load directions while the post-processing ensures manufacturability.
  • Behaviour of steel-CFRP lap joints under hygrothermal cycles and sustained
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): David Hartanto, Ehab Hamed, Ankit Agarwal, Stephen J. Foster The long term durability of FRP repaired steel structures is crucial for their safe use and effective design. Past studies that investigated the durability of steel-FRP single lap joints have focused on their response under extreme temperature and curing conditions, but without representing the actual on-site conditions for typical civil engineering applications. This paper presents an experimental investigation into the effects of hygrothermal cycles and sustained loading on steel-CFRP bonded lap joints under typical environmental conditions. A total of 72 lap joints were exposed to five hygrothermal cycles and sustained loading conditions. Specimens that survived the long-term loading were immediately tested to failure for evaluating their residual strength. The temperature cycles ranged from 15 °C to 50 °C and the relative humidity ranged between 40 and 70% under different combinations. These practical ranges of hygrothermal cycles were combined with practical curing temperatures and curing times. Sustained loads that equal to 30% and 50% of the failure loads were also applied. The results show that exposure to hygrothermal conditions only has little impact on the bonding strength. However, when hygrothermal and sustained loading were applied simultaneously, the bond strength of the lap joints was significantly affected in some circumstances.
  • Symmetry representations and elastic redundancy for members of tensegrity
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): Yao Chen, Jian Feng, Hengzhu Lv, Qiuzhi Sun Unexpectable damage of a member may cause a significant change in the load-bearing capacity or collapse of a tensegrity structure, thus redundancy analysis is important. Nevertheless, conventional approaches generally neglect the inherent symmetry and material properties. Here, we propose a method for symmetry representations and elastic redundancy for members of tensegrity structures. The symmetry and member stiffness are taken into account. To evaluate the contribution of each member to the total static indeterminacy, irreducible representation and full symmetry subspace of every type of members are computed. Then, distributed static indeterminacy of the members can be independently obtained by a simplified process. The accuracy and efficiency of the presented method are demonstrated through examples of some well-known tensegrity structures with different symmetries. This method can offer reasonable design on tensegrity structures, which are assembled by many cables and struts with identical sensitivity to initial elongations and equal importance to load-bearing capacity.
  • Comparison of cutting mechanism when machining micro and nano-particles
           reinforced SiC/Al metal matrix composites
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): Xiangyu Teng, Wanqun Chen, Dehong Huo, Islam Shyha, Chao Lin Recently, metal matrix composites (MMCs) reinforced with nano-particles receive increasing attention from academia and industries. The cutting mechanism of nano MMCs is believed to be different when compared to composites reinforced with micro particles. This paper presents cutting mechanism comparison between SiC/Al metal matrix composites (MMCs) reinforced with micro and nano-particles using finite element method. The cutting mechanisms are investigated in terms of the von Mises stress distribution, tool-particles interaction, chip formation mechanism and surface morphology. It is found that the particles in nano size remained intact without fracture during the cutting process and are more likely to produce continuous chips, while the particles in micro size are easy to break and tend to form discontinues chips. Better machined surface quality with less defects can be obtained from nano size reinforced MMCs compared with their micro size counterparts. The model validation was carried out by conducting machining experiments on two types of MMCs and good agreements are found with the simulation results.
  • Unidirectional GFRP composite connections between precast concrete wall
           panels under simulated seismic loads
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): Trevor K. Nye, Chris P. Pantelides, Clayton A. Burningham A method of connecting precast concrete walls with Glass Fiber Reinforced Polymer (GFRP) composite sheets is investigated. The method can be used either as a seismic retrofit of existing welded steel plate connections or in new construction. The specimens consisted of two precast concrete wall panels connected with either two or four layers of unidirectional GFRP composite sheets. Eight specimens were subjected to quasi-static cyclic loads to explore the effect of the following variables on the connection capacity: concrete surface preparation; application of surface pressure to the GFRP laminate; number and orientation of GFRP composite layers; and use of carbon fiber reinforced polymer (CFRP) spike anchors. The performance of the composite connection was acceptable in terms of lateral load, lateral displacement, and shear transfer capacity. Application of surface pressure during curing of the GFRP laminate and the use of CFRP spike anchors improved the lateral load and displacement capacity of the composite connection significantly. An empirical expression is proposed to determine the capacity of the composite connection.
  • Nonlinear bending and vibration analysis of functionally graded porous
           tubes via a nonlocal strain gradient theory
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): Gui-Lin She, Fuh-Gwo Yuan, Yi-Ru Ren, Hai-Bo Liu, Wan-Shen Xiao In this paper, the nonlinear bending and vibrational characteristics of porous tubes are analyzed for the first time. Within the framework of the nonlocal strain gradient theory, a size-dependent model for the tubes with radial inhomogeneity is formulated. It is assumed that the tube is made from functionally graded materials (FGM). Employed a new model for tubes which takes into account of the shear deformation effects, the motion equations are derived with the help of Hamilton variational principle and determined by the two-step perturbation technique. The validity and feasibility of the method are verified by actual examples. The effects of different parameters such as scaling parameters, porosity volume fraction, power law index and inner-to-outer radius ratio on the nonlinear bending and vibration behaviors of the porous tubes are particularly discussed.
  • Basalt scale-reinforced aluminium foam under static and dynamic loads
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): Jun Li, Chengqing Wu, Hong Hao, Zhongxian Liu, Yekai Yang In this paper, mechanical performance and deformation behaviour of basalt scale-reinforced closed-cell aluminium foams are investigated. Quasi-static uniaxial compressive tests on the constitutive alloy material reveal that after basalt scale reinforcement, the alloy elasticity modulus and yield strength show noticeable enhancement. Quasi-static compression tests on the foam material show that while basalt scale-reinforced aluminium foam has higher plastic crush stress and plateau stress, the densification strain is lower than non-reinforced foam. A method based on energy absorption efficiency is adopted to accurately measure the densification strain for both foam materials. In the subsequent split-Hopkinson pressure bar tests, dynamic compressive behaviour of basalt scale-reinforced aluminium foams with relative densities ranged from 14% to 33% is studied experimentally under strain rate ranging from 480/s to 1720/s. Clear material rate sensitivity is noted from the dynamic tests. The results indicate that the plateau stress of aluminium foam increases with relative density and strain rate. In addition, with the increase in strain rates, an increase in the energy absorption capacity is observed and this characteristic is beneficial when the foam material is used to absorb impact energy. A mesoscopic model based on the X-ray CT for the aluminium foam material is developed. The simulations and the test data agreed well for the quasi-static loading case. However, it is noted that the mesoscale model without consideration of the base material rate sensitivity and the entrapped gas underestimated the strength enhancement under dynamic loading scenario.
  • Laboratory investigation on the buckling restrained braces with an optimal
           percentage of microstructure, polypropylene and hybrid fibers under cyclic
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): J. Esfandiari, E. Soleimani Normal braces have a high stiffness but are buckling under compressive strength and have very low ductility. To overcome these disadvantages in recent years, a buckling restrained braces system has been used. In this study the optimal percentage of Microstructure, Polypropylene and Hybrid Fibers were determined by using tensile and compressive test, the results exhibited that the highest rate of tensile and compressive strength were occurred in the case of reinforced concrete with polypropylene fibers and the composition of polypropylene and metal fibers as known hybrid fibers compared to the non-fibrous concrete for test specimens containing (0.15–0.3) percent polypropylene fiber and reinforced concrete with the composition of polypropylene and sinusoidal fibers related to test specimens containing (1.5%) metal fibers. Also, the results of scanning electron microscope imaging of concrete core sheaths obtained from fiber concrete in this study showed that fibers play a micro role in concrete. In addition, this research the effect of using optimum amount of fibers in the concrete sheaths in the buckling restrained braces were investigated. For this purpose, 6 samples of buckling restrained braces were made and examined in three modes. Concrete sheaths of buckling restrained braces without fibers, with polypropylene fibers and composition of polypropylene and sinusoidal metal fibers were the three modes. The samples made were then shifted to the intended location and installed in the laboratory under the loading protocol of BD/SAC – 02/97, also by applying the horizontal displacement contained in this protocol, the applied load and the amount of related peripheral displacement were calculated. Backbone, loading cycle-force, horizontal displacement – lateral displacement, push over curve and bilinear behavior model were finally drawn. By examining the results, it is shown that the maximum number of loading cycles, the coefficient of ductility, the energy absorption, and the maximum amount of applied force in the specimen produced by the composition of polypropylene and sinusoidal metal fibers are accrued.
  • High-power laser resistance of filled sandwich panel with truss cores:
           Ablation mechanisms and numerical simulation
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): Jiangtao Wang, Wu Yuan, Yuwen Liu, Hongwei Song, Chenguang Huang A new function of filled sandwich panel with truss core, superior high-power laser resistance, is reported. When filled with carbon powder-reinforced silicone resin composite, which is an ablative material, the panel exhibits superior high-power laser resistance to monolithic plate with equal areal density. This paper revealed the detailed mechanisms and reproduced the process with numerical simulation. FIIR, SEM-EDS, and TG/DSC analyses on the virgin filler material and ablation residues are conducted to investigate the thermo-physicochemical process of the filler material during the laser ablation. Considering pyrolysis, oxidation, and phase change in the laser ablation process, a 3D numerical model is developed by using the finite element method. The temperature field and ablation morphology obtained from the numerical model agree with those from the experiment. The ablation evolution process, pyrolysis effect, and laser resistance mechanism of the filled sandwich panels with truss cores are evaluated based on the present model.
  • Prediction of critical thrust force for tubular composite in
           drilling-induced delamination by numerical and experimental analysis
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): H. Hocheng, C.C. Chen, C.C. Tsao Delamination is among the major concerns of the composite structures. Drilling often causes delamination damage at the exit of the hole when the drilling thrust is larger than the critical interlaminar strength of the composite laminates. The curved laminates endure even lower drilling thrust than the flat plates. The current study provides both numerical and experimental analysis to reveal the development of delamination initiation along with the drill movement downward. The last ply under the drill bends in response to the applied drilling thrust force until the threshold when the interlaminar strength cannot sustain and the crack starts to grow. Such onset of drilling-induced delamination can be clearly predicted by the current method. The calculated critical thrust force at the onset of delamination is compared with the experimental study and finds agreement. Knowing the material properties, the hole size and the tube diameter, one can predict the critical thrust force in drilling the composite tube and therefore able to select the proper drilling parameters including the feed rate and rotational speed for maximizing the production rate while avoiding the delamination damage during drilling a composite tube.
  • Numerical investigation of composite laminates subject to low-velocity
           edge-on impact and compression after impact
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): Solver I. Thorsson, Anthony M. Waas, Mostafa Rassaian In this paper, a shell based finite element (FE) model previously introduced for capturing the face-on impact and compressive strength after impact (CSAI) response of composite laminated structures is evaluated for predicting the dynamic response and damage due to edge-on impact and the resulting CSAI. The model utilizes an in-plane progressive damage and failure material model, Enhanced Schapery Theory (EST), for modeling the full field damage and failure of a single lamina in the 1–2 plane. The material model captures the pre-peak matrix non-linearity due to micro cracking using Schapery Theory (ST). The Bažant-Oh Crack Band (CB) model is utilized for matrix cracking and fiber rupture at the lamina level. Discrete cohesive elements are used for delamination initiation and propagation. Edge-on impact data for a range of impact energies is used for evaluating the models capability. The predicted impact damage state of the laminate is used for acquiring predictions of the CSAI of the laminate. The model predictions show promising results for the impact and CSAI response of an edge-on impacted coupon. The paper discusses the strengths of the model, the issues encountered, as well as topics for future study.
  • Comparison of low velocity impact modelling techniques for thermoplastic
           and thermoset polymer composites
    • Abstract: Publication date: 1 November 2018Source: Composite Structures, Volume 203Author(s): X.C. Sun, L.F. Kawashita, A.S. Kaddour, M.J. Hiley, S.R. Hallett This paper presents comparisons between experimental and numerical studies of low-velocity impact damage for thermoplastic (IM7/PEEK) and thermoset (IMS65/MTM) carbon fibre reinforced composites. The experiments were conducted at two key impact energies (8 and 30 J) under identical conditions allowing a systematic comparison to be made. Three LS-DYNA Finite Element Analysis (FEA) models (standard, continuum damage mechanics (CDM) and discrete) were implemented, all using cohesive interface elements for delamination. The role of Mode II fracture toughness is highlighted. The predictive capabilities of different modelling techniques are compared and discussed and the CDM model gave better correlation with experiments. Fibre failure was predicted by the numerical approaches. The thermoplastic materials did not show noticeably superior behaviour to the thermoset materials and were governed by unstable delamination damage propagation for the same impact energy.
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